GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted
Musings of an Energy Nerd

Heat-Pump Water Heaters Come of Age

Now that pilot studies show that installed heat-pump water heaters are performing fairly well, it might be time to buy one

Heat-pump water heaters are about twice as efficient as electric-resistance water heaters. They are also taller; this Voltex model from A.O. Smith is almost 7 feet tall.
Image Credit: A.O. Smith

UPDATED on October 26, 2018

The least expensive way to heat domestic hot water is with natural gas. Homes without access to natural gas usually choose an electric water heater, since electricity is generally cheaper than propane.

Although most electric water heaters use electric resistance elements to heat water, a more efficient method uses a heat pump — in other words, a device that heats the water using a compressor like the one found in a refrigerator or air conditioner. While a refrigerator transfers heat from the interior of the refrigerator to the room where the refrigerator is located — in effect, heating the room — a heat-pump water heater transfers heat from the room to a tank of water — in effect, cooling the room.

Heat-pump water heaters need backup elements

Compared to an electric-resistance water heater, the main benefit of a heat-pump water heater is energy efficiency. While the efficiency of electric resistance elements is 100% — all of the electrical energy sent to a resistance element is converted into heat — the efficiency of an air-source heat pump can be as high as 250%. The heat-pump isn’t making heat — it’s transferring heat from the air to the water. A heat pump is capable of transferring more energy than the energy required to run it.

The type of heat pump used for heat-pump water heaters can’t heat water as quickly as electric resistance elements, however. While the electric-resistance elements in a typical water heater can heat 20 gallons per hour, a heat pump can only manage about 8 gallons per hour (or even less, if the ambient air temperature is below 68°F).

To make up for this basic deficiency in heat-pump performance, heat-pump water heaters are equipped with electric resistance elements that are energized whenever the heat pump can’t keep up with the demand for hot water.…

GBA Prime

This article is only available to GBA Prime Members

Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.

Start Free Trial


  1. YXeXWBqjE8 | | #1

    "The least expensive way to heat domestic hot water is with natural gas."

    Not if you live in an area where solar water heaters are effective, which covers a large chunk of the US population. Solar energy is free after the initial installation cost of a solar water heater.

    Jason Szumlanski

  2. GBA Editor
    Martin Holladay | | #2

    Response to Jason Szumlanski
    No energy researcher in the country agrees with your claim that solar thermal systems can make hot water for a lower cost than natural gas. Solar thermal systems have a payback period of 58 to 76 years, according to researchers from Steven Winters Associates -- a time frame that is longer than the expected lifetime of the equipment.

    For more information on this topic, see Solar Thermal is Dead and Solar Hot Water.

  3. user-1121160 | | #3

    Another Option
    Another heat-pump water heater option, especially for those who have an existing electric or gas hot water heater or insulated hot water storage tank, is the Nyle Geyser. There is an article and discussion about using a Geyser with a Marathon electric hot water heater on Marc Rosenbaum's Thriving on Low Carbon blog:

  4. GBA Editor
    Martin Holladay | | #4

    Response to AJ
    I look forward to a more substantive post from you, AJ.

    If you are going to accuse me of writing a slanted article, as well as writing an article with "missing information," please help GBA readers by identifying the slanted statements and the missing information.

    [Later edit - 4/23/12 : I see that A.J. has edited his comment to remove his accusation that the article is slanted and that the article is missing information. Thanks for the change, A.J.]

  5. GBA Editor
    Martin Holladay | | #5

    Response to Don Purington
    While this article focuses on integrated HPWHs (units that include a tank), you're right that other options are available, including add-on units like the Geyser.

    Thanks for providing the link to Marc Rosenbaum's blog. I've been in touch with Marc on his monitoring studies. In addition to the data he has been collecting on the Geyser in his basement, Marc has also been monitoring a Stiebel Eltron integrated HPWH at a client's house.

  6. zimmerdale | | #6

    noise reduction
    I'm concerned about the noise factor of putting one in my finished basement. I don't have a suitably large room to isolate the heater from the bedrooms or family room, just a utility closet. If the exhaust air can be ducted outside, could the intake air be ducted into a small sound dampened compartment housing the heater? The compartment could even be directly supplied from the ERV.

    This is a small Passive House project I'm working on for my family, by the way. Just trying to think creatively.

  7. GBA Editor
    Martin Holladay | | #7

    Response to Jason Miller
    I think you're on the wrong track. These units shouldn't be installed in a closet, and trying to come up with ingenious ducted solutions to a basic error (putting an appliance where it doesn't belong) makes no sense.

    You should buy a well-insulated electric-resistance water heater.

  8. seecrikJfX | | #8

    Attic Installation
    What are you thoughts on installing a heat pump water heater in a "conditioned" attic?

    I'm a homeowner planning to build a new single-story home this summer with spray foam insulation in the walls and on the roof decking. I'm shooting for a pretty tight envelope. The attic should have plenty of physical space for the relatively large heat pump unit, but I'm not sure I can adequately deal with potential vibration issues of a heat pump unit.

    Any thoughts?
    Cameron Moore
    Abilene, TX

  9. user-1044812 | | #9

    One clever idea....
    While I think in our local climate HPWH are not a good fit, one place they can really do well is in light commercial. With some planning, they can be located in, or share air space with, a server closet - effectively cooling the equipment and scavenging heat from the high ambient temperature. The draws are low so the resistance heat should not kick in. In fact, the Building Performance Center in Bellingham has done exactly this.

  10. GBA Editor
    Martin Holladay | | #10

    Response to Cameron Moore
    Once you install spray foam on the underside of your roof deck, your attic becomes part of your home's conditioned space. There are many advantages to this approach; for example, you can turn your attic into a bedroom if you want, as long as your local building inspector approves.

    If you put a HPWH in a conditioned attic, its thermal performance will be the same as if you put it anywhere else within your thermal envelope. After all, inside is inside -- especially if (as your write) you are planning to build a well insulated house with a tight envelope.

    During the winter, you can expect your furnace or boiler to work a little harder to make up for the heat that the HPWH robs from your conditioned attic.

  11. GBA Editor
    Martin Holladay | | #11

    Response to Jim Hassi
    Yes, I've heard of the "HPWH in the server room" idea before. It makes a lot of sense.

    Here's another twist I thought of -- I haven't heard of anyone doing it yet, but it's intriguing: attach a duct to carry the HPWH exhaust to a grille behind your refrigerator. If you blow cool air over the coils at the back of your refrigerator, the coils will heat up the exhaust air slightly, and the cool air will improve the refrigerator efficiency.

  12. seecrikJfX | | #12

    Response to Martin Holladay
    Thanks for confirming what I was thinking about the advantages of putting the HPWH in a conditioned attic, but what are your thoughts about potential noise and vibration issues of putting the HPWH in the attic? If I put the HPWH in my attic, it will have to sit over our living space -- most likely somewhere between the dining room and the master bath.

  13. GBA Editor
    Martin Holladay | | #13

    Response to Cameron Moore
    Only you can decide where the sound of operating equipment will irritate you. Do window-mounted air conditioners drive you crazy or not? Assume that it will sound like a window air conditioner. Of course, you'll have a floor assembly between you and the noise.

    Some people are very sensitive to the sound of mechanical equipment. Other people never notice.

  14. scottcmccullough | | #14

    Radiant Floors
    These articles and discussions are great, hard to find good information like this elsewhere.
    I'm wondering how well a HPWH would work for DHW in conjunction with low temperature radiant slab heating. The small house we are designing and building is approx. 1600 SF plus basement, woodstove for primary heat, radiant as backup. The comments from Steve Winter Associates describe the COP going up with more water use (to a point), and the COP going down with large volume draws. How might DHW plus a radiant slab fit into this equation? Could the HPWH keep up with a constant 90-95 deg. draw for the slab?

  15. GBA Editor
    Martin Holladay | | #15

    Response to Scott McCullough
    There are two problems with your idea:

    1. The type of HPWH under discussion can only heat about 8 gallons of hot water per hour; the output is insufficient for space heating.

    2. Obviously, an air-source heat pump moves heat from the air around it to the water in the tank. This won't help you provide space heat if the HPWH is located indoors -- gathering heat from the air just cools the house instead of heating the house. The heat you have gathered from the air is then sent back to warm the air you just cooled; the net effect is to heat the house slightly because of the waste heat thrown off by the compressor motor. It makes more sense to use an electric resistance heater than to do that.

    Your idea might work if the HPWH were located in your garage -- but only if you were heating a tiny house in a warm climate.

    In short, if you want to use an air-source heat pump for space heating, buy a ductless minisplit.

  16. GBA Editor
    Martin Holladay | | #16

    Notice to readers
    I'll be on vacation next week (April 14-21), so don't be surprised if I am unable to answer questions posted here. If the questions pile up, readers will have to be patient. I'll return to my office on April 23.

  17. GBA Editor
    Martin Holladay | | #17

    Response to AJ
    1. I never claimed that HPWHs save water.

    2. Although most Americans can afford the cost of heating domestic hot water, that fact does not mean that we shouldn't look for efficiency improvements.

    3. I agree that HPWHs cost more than electric-resistance water heaters; in fact, my article tried to quantify the incremental cost. I quoted Robb Aldrich, who calculated that the incremental cost of a HPWH compared to an electric-resistance water heater ranges from $1,400 to $2,700.

    4. I agree that HPWHs are more complicated than electric-resistance water heaters, which is why my article includes a section discussing equipment longevity. The jury is still out on that issue.

    5. I agree that, in light of their higher price, there is reason to believe that HPWHs require more resources to manufacture than electric resistance water heaters.

    In short, AJ, I think you'll find most of the information you need to make a decision about whether a HPWH makes sense for you by reading the article.

    As my article makes clear, HPWHs don't make sense for many homes. Just because the puppy has come of age and is now a mature dog, doesn't mean you need to rush out to the nearest pet store and buy one.

    A HPWH isn't a cure-all; it's just an appliance, like a boiler, HRV, or dishwasher. Not every house needs one. But for those who are considering buying one, my article provides information to help people figure out whether a HPWH makes sense for their house.

  18. Expert Member
    Dana Dorsett | | #18

    The unanswered space heating impact question...
    In a heating dominate climate, locating the unit in conditioned space, the fraction of the heat pulled from the surrounding space adds to the load on heating system, and those BTUs are paid for at the fuel cost & efficiency of your space heating source. In a high-R passive solar house this might be pretty good, but for the typical New England home, not so much. At current prices propane & heating oil in typical-efficiency burners running a 2.35EF heat pump water heater is on a par with (or would even exceed) the cost of just heating it with electricity in a 0.90EF tank. In this climate putting it in an unconditioned garage would be even lower efficiency/higher cost.

    Inside of conditioned space or a semi-conditioned basement, for maybe 4 months out of the year it would be a net win, lowering the cooling load. Whether that breaks even with the uptick on space heating costs for the other 8 months of the year is not something that can be calculated on a napkin (or even a spreadsheet) without real experimental data to back it up.

    Until those factors are measured empirically, recommending them for use in heating-dominated climates is premature, at least for homes with expensive space heating fuels, and even for those with less-expensive fuel, the annual savings based on EF numbers (or third-party testing in-situ that measures only the power used by the water heater, ignoring the space heating impact) are clearly overstated.

  19. GBA Editor
    Martin Holladay | | #19

    Response to Dana Dorsett
    I agree with your conclusion that HPWHs don't make sense for many houses, especially cold-climate houses. In many cases, a well-insulated electric-resistance water heater is a perfectly reasonable choice.

    That said, I think your conclusion that a HPWH in a New England basement would only be a "net win" for 4 months of the year is overly pessimistic. However, I'm not pushing these devices. I'm presenting the currently available data for anyone who's interested; if you're skeptical of the benefits, stick with electric resistance.

  20. user-626934 | | #20

    Ducting HPWH to refrigerater coil

    I just visited Daniel Ernst at his soon to be completed house in Virginia. He's planning on doing exactly what you described....using an AirTap HPWH (that is set up for optional ducting) and dumping the cool air behind the fridge. I'm not sure it will lead to a measurable difference in energy use for the fridge, but the physics certainly make sense...and if there's anywhere it's OK to dump cool air in the wintertime, this would be the spot!

  21. GBA Editor
    Martin Holladay | | #21

    Response to John Klingel and John Semmelhack
    I got the behind-the-fridge idea a few days ago -- but it makes sense that I wasn't the first person to think of it. Of course, the biggest drawback is that the refrigerator compressor and the HPWH compressor don't necessarily come on at the same time.

    Many people have imagined an integrated appliance -- a heat-pump water heater cum refrigerator -- but the problem always boils down to the fact that the loads don't necessarily coincide.

  22. gusfhb | | #22

    re fridges etc
    I am still waiting to see the mad HVAC tech with a fully integrated heat pump house. heat ac hot water fridge. IIRC Mitsubishi makes multi head units that can move the heat around, IOW, cool the server room and heat the next room.

    RE: AJ you have completely ruined my fun today, I was going to comment that HPWH sounded like a 'gadget' and quickly run away..................I am certain you have a point but you have not fully elucidated it, please do.

  23. cSEmF2Yopx | | #23

    benefits of exhaust air ducting
    I'd like to add a comment to my quote in the article. Ducting of exhaust air is beneficial from a customer comfort point of view and NEEA is developing guidelines for the installation of units with and without ducting depending on installation location. Without the ducting, all of the cold air from the HPWH is being used to directly cool down the surrounding area. If this is a utility room near a living space, it will be like you put a 3/4 ton air conditioner into the middle of the room. We've heard complaints about this. While it is true that the make up air will have to come from the outside, and in very cold climates the incoming air may be colder than the air exhausted from the HPWH, the "coldness" impact on the house will be more distributed and there are likely to be fewer complaints from consumers. The interaction with whole home space heating is complex, and we are still doing the modeling and field studies. Preliminary indications are that ducting of cold air makes sense for many if not most installations of HPWHs in conditioned spaces.

  24. Expert Member
    Dana Dorsett | | #24

    Overly pessimistic? I doubt it. Response to Martin
    In southern New England coastal cities such as Boston or Providence the mean binned-hourly outdoor temps are only above 65F (the approximate heating/cooling balance point for "typical" single-family homes) for 4 months out of the year. For more northerly or inland locations it's 3 months or less.

    The rest of the time there is a net heating load just from weather considerations for most homes, and heat pump water heaters just add to that load.

    You can't cheat the laws of physics- with the water heater inside of conditioned space the non-electric fraction of the heat going into the water is coming out of the house, ultimately supplied by the heating system. Even in an insulated basement with an uninsulated slab the amount of heat you can get of of the earth through the slab is pretty limited, with <50f subsoil temps. (my basement slab in worcester measures the low to mid-50s even with room heated constantly 65f.) so cost of heating water is still highly dependent upon & efficiency space fuel equipment. it's a huge elephant that needs careful consideration before making broad recommendations, particularly for locations us climate zones 5 higher very modest average cooling loads.

    In my case the sensible cooling load is miniscule, but a heat pump water heater would take most of the latent load off, currently handled by a dehumidifier. But were I heating with oil or propane it may have a higher net operating cost overall, since the cooling season (even latent-cooling season) is less than 4 months, most years.

    But the full model isn't napkin-math (or even lipstick-on-the-mirror math :-) ), and it SURE isn't anything as simple as average operating EF ratios.

  25. jklingel | | #25

    Not me
    "Response to John Klingel and John Semmelhack" Just for drill, I have not posted yet, but I don't mind my name being mentioned if there is no swearing associated therewith. : )
    Dana D: I am with you about cheating physics, (this concept was mentioned in another article here about these machines). I think a fundamental point needs to be STRESSED more heavily when writing about these things. That point is this: You must consider the source of the heat that these transfer to water. If the source of said heat is your oil boiler, than forget buying one. If the source is "free" (computer room, solar, etc) than by all means run the numbers and see if one makes sense. That idea ("...(cooling) a side effect which is beneficial in hot weather but potentially problematic during the winter...") is mentioned in the article, but I feel it needs to be stressed, as it is the critical factor in deciding whether or not to use one, as I see it. In my zone (8) I suspect they are a waste of time in most houses. In many other locations, it sounds like they would work great. It all hinges on who's paying how much for the heat they transfer.

  26. djt76 | | #26

    Get real people
    Wow this was exactly what i needed to see, thanks everyone for the comments! I tend to side with realism whenever possible. My plumber tells me to forget about it,a lot like AJ. In my experience the natural developement of the most commonly used building products are the way they are for really good reasons. When i was a kid i was going to re-invent stick framing too! Kids they never learn...

    Reducing the cost of electricity would make theses options work. If you're all about reducing fossil fuels, then get PV panels and get the best electric resistence WH and be done with it.

    How about an article about the totaly under reported solar thermal conversion to electricty technoloy acheiving 35% and possibly 60% conversion to electric power. Now there's the game changer everyone's looking for. Does anyone know what i'm talking about?

  27. watercop | | #27

    Response to several
    I've had an early generation Geyser operating in my basement for 2-3 years. It is mated to an 80 gallon tank and supplies a household of 4-5 (one partime teenager). My data shows it operating at an EF of around 2.0, which is consistent with its design (pump and external heat exchanger)

    It is noisy...MUCH noisier than the GE Geospring units I've put in the field. I'm told newer Geysers are a bit more refined. The niche most suitable for a Geyser is a client with a newer OVERSIZED water heater, 65+ gallons. The only 80 gallon HPWH I know of is still priced over $2k, leaving plenty of room for a Geyser to be deployed at lower cost.

    In warmer clients, a 50 gallon HPWH should be able to serve a 3 person household, but we only have to raise incoming water by 40-50 degrees. I agree that the much steeper rise needed up north combined with longer recovery times militates in favor of larger tank sizes for best efficiency and client satisfaction.

    Comparing an Integrated HPWH to a 3/4 ton AC is a bit of a reach. Under 5 kBtuh is more like it, in terms of all of compressor noise and power, air flow, and net refrigerative effect. For every 1000 Btu transferred to water, only 600-700 Btu comes from surrounding room.

    I agree with the advice to upsize an HPWH. I disagree with the advice to operate it with a setpoint much above 120*F. Higher setpoints substantially reduce efficiency (EF or COP, take your pick) and increase load on compressor and refrigerant pressures.

    I believe the saving calculation comparing HPWH to electric resistance in New England is flawed by the fact that electric resistance is less common in New England. A real potential for savings occurs if a HPWH allows shutting down a boiler operating all summer just to heat an indirect tank. A boiler so operated has a very low EF all summer, possibly 0.25 or even less, depending on number of people in the home.

    All that said, I agree that HPWH may not make sense much above C-Zone 4, unless there is a special circumstance such as a woodstove or similarly cheap source of heat already in place to offset the HPWH's needs. High electricity cost would militate against HPWH as well.

    Finally, a word of caution about some model HPWH - I believe that the AirGenerate models operate with a high pressure refrigerant line directly immersed in the tank of water. This risks potable water becoming contaminated with refrigerant oil or even residues from a burnt out compressor. Most other designs separate refrigerant lines from direct contact with water such that a refrigerant leak would be to atmosphere.

  28. LVjepxXQB9 | | #28

    Lovely Discussion
    I like how everyone is open to someone else's views/experiences despite having their own. Martin always seems to have a very well documented answer to people's questions but I'm sure he also learns every now and then from posted comments. Discussion is a great tool to get well suited information out there.

    Side note: GBA Advisor seems redundant... like PIN Number.

    As for my own views on the subject, it appears that from all the evidence shown, HPWHs only seem to make sense in places with year-long cooling and limited access to natural gas. If I had a home in Mexico I'd probably consider one. Drain water heat recovery is definitely more attractive for DHW savings.

  29. 5LKAjaMB6v | | #29

    Heat Pump Water Heaters
    I am anticipating replacement of my 13-year old electric hot water heater which is located in a separate 750 sf utility room within my garage. We currently suffer fairly long wait times for hot water delivery to most faucets in our two-story house. Would a heat pump water heater make any difference without making piping changes? I do not want to use a hot water circulation pump.

  30. [email protected] | | #30

    I think I have found the perfect instance for the HPWH-

    I have some clients in Maine and here is are the details:

    1. This a 2 bedroom home on a slab- home insulation is average
    2. The home has radiant heat, but the boiler is in the attached garage. The boiler is a 15 year old oil boiler and it has a coil that heats the hot water for the home.
    3. The home is a radiant heated slab. The boiler stands about 6' away from the joining garage and home wall and the raidant dist. center is about 9' away. All the radiant supply and return lines make this garage a balmy 80 degrees in summer and over 60 in winter. The garage is well insulated.
    4. The HPWH would steal all of this wasted heat, cool the garage especially in the summer and keep the boiler off completely all spring and summer.

    I was ready to install an indirect heater 2 weeks ago, but now I am thinking this is a better plan.

    Thanks for any feedback.

  31. Expert Member
    KOHTA UENO | | #31

    Attic Installation/Cameron Moore

    If you put a HPWH in a conditioned attic, its thermal performance will be the same as if you put it anywhere else within your thermal envelope. After all, inside is inside -- especially if (as your write) you are planning to build a well insulated house with a tight envelope.

    Hi Martin--when I have wandered around conditioned attics that have fair slopes (e.g., 10:12, 12:12), I've noticed that there's some thermal stratification going on. In the really tall ones, I've found that the bottom of the attic is close to room temperature (~75 F), while up near the peak is a warm 80-85 F. So there could be some benefit--in a cooling-dominated climate--to putting a HPWH up in that attic, to "soak" the additional heat coming in during the summer. Of course, there are all the negatives of putting a water heater above your head (flood damage when it blows out, wresting the damn thing up the attic hatch). On the other hand, it's common practice in parts of Texas.

  32. user-1006269 | | #32

    Timely thread. I just finished shooting a new installation video for the Geyser yesterday.
    There are some apples and oranges issues between the units being discussed.

    I live with an earlier add on unit made by Nyle, the manufacturer of the Geyser.
    It is louder than the newest Geyser unit but not objectionable. We have an early Geyser in our
    shop. It is quiet enough that I can use the phone next to it and not have anyone comment on it.

    HPWHs have a place in the world. It seems to me that the stand alone units have a lot to offer since they can be recycled onto other tanks if necessary and/or can be taken by the owner if moving.

    The dehumidification that all units offer can be significant. The unit I use operates only in the summer when I am not using my gasification wood boiler. It dehumidifies and cools the first floor of my home. Since I live on the coast of Maine, this is an advantage. It operates into a 350g tank and costs about $20 a month to operate here in Maine with our 18 cent/kw electricity. I cannot wait for off-peak rates!
    That 350g tank is going to make this a great deal!

    Having handled several different units, it seems to me that the build quality of the Geyser is substantial and serviceable in that the controls are hand wired and can be easily repaired. Many other units have controls that are potted in epoxy which is not serviceable unless you replace the entire control.

    All in one units are certainly attractive from an initial cost point of view but will not be re-usable if the tank fails.
    This requires one maintaining their anode rod in the tank (something not many folks do).
    AirGenerate has a special anode rod that is easy to maintain, since their stand alone unit is not going to be moveable to a new tank.

    We have used Geysers with our Heat Bank storage tanks with excellent results.
    This allows the solar or wood boiler customer to use their large tank coupled to a Geyser for backup in the summer or other times of the year when the alternative system is not generating heat.

    We sell the Geyser for about $1150. Not cheap but a very solid unit.

    Tom Gocze

  33. kevin_in_denver | | #33

    Reply to Edgar Lopez
    Congratulations Edgar, I think you boiled down this entire topic in one sentence:

    " it appears that ..., HPWHs only seem to make sense in places with year-long cooling and limited access to natural gas."

    I would add this is only for retrofit situations.

    In low energy new construction, however, there is a lot of motivation to forgo all natural gas to the house:

    1. Gas taps cost money ($1000-$15,000)
    2. Natural gas will cost you a $8 to $25 per month service fee even if you don't use any gas.
    3. Because of the the service fee, a low energy home will use an air-to-air heat pump instead of a gas furnace.

  34. BsDwTKPfmJ | | #34

    Heat Pump Hot Water Services
    Hi, I live in Zone 4 in Australia and before you think all of Australia is HOT and therefore not relevant, I hasten to advise you this is not the case. I live 75km (45 miles approx) inland from Melbourne on the south coast of Australia. Our latitude is 37.5 degrees south or about the same as San Francisco. However, we also live in the mountains at an elevation of 450 metres (about 1500 feet). In other words, we have warm, occasional hot days in summer and cold, wet winters with a number of mornings where the ground is covered in frost and it has dropped below zero Celsius by a few degrees overnite.

    I use a Heat Pump Hot Water Service that is outside and only comes on at night. Its noise level is 58db, it use 1.47kw of power and delivers 5.8kw of heat. That is about 400% efficient. The tank is Stainless Steel with polycarbonate covered insulation. I am delighted with its efficiency and how my electricity bill for water has dropped by 75%.

    Here in Australia, as it seems also in North America, Heat Pump Hot Water systems are bagged as expensive, noisy, inefficient, etc, etc, etc. I bought a top of the line model, cost $4,400.00 Aus ($4,563.US) and another $500 for the plumber and Air Conditioner licensed electrician.

    I bought a Siddons Solarstream Heat Pump H.W. S. and hear is a review site Company site is Oh mine also works when the temperature drops to -5C (23F), It might work all nite when it's cold but who cares. The reason mine is wired to work at nite only is that the overnite power bill is 10cents/KwHr compared to 30c/Kwhr during the day but there is an over ride button to push if H.W. runs out during the day which it never has. Had the unit two years and I'm delighted. By the way, would never touch a Rheem HP.H.W.S. Here in Oz, they are noisy, very inefficient and can't work below +5C. Regards, Stan.

    P.S.: see also. They market Siddons as a Skyline across Oz but they also do HP hydronic slab heating. I really think H.P. are brilliant if you haven'y guessed already!

  35. user-1091869 | | #35

    Not as new as it seems!
    My father installed a similar device in our new house in the UK in 1957 - a Ferranti fridge-heater that used heat extracted from the larder / pantry to heat the water. I can't find a detailed description on-line - although I have in the past - but I have found one article that quotes a heating capacity of 1.2 kW in the summer and 0.7 kW in the winter. It did not provide enclosed storage space like today's fridges - it was essentially a heat exchanger with the capability of making ice.

    Its problem was that recovery was very slow - we couldn't take more than one bath in an evening! This problem was later resolved by adding an electric resistance heater.

    I've always been surprised that no-one has further developed water heaters that use heat from fridge/freezers (or heat extracted from air-conditioning units) - at least for warmer climates. Today's large fridges and freezers must require more cooling than did our larder - and thus I'd think that the potential to heat water should be there?

    I also thought of supplying and/or extracting air behind the fridge - but not until after I'd completed our kitchen... In the winter the heat would be more usefully distributed to the remainder of the house, and in the summer the fridge would likely run more efficiently.

  36. user-659915 | | #36

    Response to Edward Acker

    I am anticipating replacement of my 13-year old electric hot water heater which is located in a separate 750 sf utility room within my garage. We currently suffer fairly long wait times for hot water delivery to most faucets in our two-story house. Would a heat pump water heater make any difference without making piping changes?

    Answer: No.

  37. user-1097504 | | #37

    a good match with ground source heat pump?
    seems this could be a good match with a ground source heat pump heating system? especially in a new build, highly insulated, that has a basement with insulated radiant floors?

    also, people don't seems to talk much about moving away from fossil fuels, i wonder why? isn't that or shouldn't it be one of the objectives of of 'green building'?

    i am new to all this, so thanks for your candid thoughts.

  38. 5C8rvfuWev | | #38

    Response to Edward Acker
    Have you considered adding point-of-use tanks or elec resistance dhw backup for the main heater? A small tank (or tankless) in a closet or under a counter could supply hot water with the main supply feeding it; it would give hot water close to taps and not let much go down the drain. Your situation sounds like it would be worth considering.

  39. GBA Editor
    Martin Holladay | | #39

    Response to Dana Dorsett
    You wrote, "In southern New England coastal cities such as Boston or Providence the mean binned-hourly outdoor temps are only above 65F (the approximate heating/cooling balance point for "typical" single-family homes) for 4 months out of the year. ... The rest of the time there is a net heating load just from weather considerations for most homes, and heat pump water heaters just add to that load."

    1. If you prefer not to install a HPWH, by all means don't buy one.

    2. Most homes don't require space heating systems to be turned on when the outdoor temperature drops to 64 degrees F, because internal loads (refrigerator, TVs, computers, lighting) provide plenty of heat until the thermometer drops several degrees lower than the 65 degrees you specified.

  40. GBA Editor
    Martin Holladay | | #40

    Response to Edward Acker
    Q. "We currently suffer fairly long wait times for hot water delivery to most faucets in our two-story house. Would a heat pump water heater make any difference without making piping changes?"

    A. I agree with James Morgan -- the answer is no. For more information on possible solutions to the piping problems you mention, see All About Water Heaters.

  41. GBA Editor
    Martin Holladay | | #41

    Response to Bo Jespersen
    I agree that a HPWH might make sense in the situation you describe -- a house with a boiler located in an attached, insulated garage. If the garage temperature ranges from 60 degrees to 80 degrees, then using a HPWH to suck up some of that wasted heat might make sense.

    This type of scenario makes me nervous, however, because the boiler is obviously installed in the wrong place, and a lot of energy is now being wasted. It would be a lot better to just design a better heating system, rather than throw another new appliance (the HPWH) at the situation -- a situation in which no one with any sense was involved in the original heating system design.

  42. GBA Editor
    Martin Holladay | | #42

    Response to Kohta Ueno
    I think you have done a good job of presenting the pluses and minuses of installing a HPWH in a conditioned unvented attic.

    There may be some extra heat up there to suck up (although if there is, that's a sign that the spray foam installer skimped on insulation thickness and R-value -- a major problem in the spray-foam industry), but attics are a really lousy place to put a water heater (difficulty of access, difficulty of maintenance, and risk of flooding).

  43. GBA Editor
    Martin Holladay | | #43

    Response to Janet Bergman Wilkinson
    Q. "It seems this [a HPWH] could be a good match with a ground-source heat pump heating system?"

    A. Actually, no. If you plan to install a ground-source heat pump, you don't need a heat-pump water heater (which heats water with an air-source heat pump). You want to choose a ground-source heat pump that includes a desuperheater. A desuperheater is basically a device that makes domestic hot water using the ground-source heat pump as the source of heat. (After all, if you have already bought a ground-source heat pump, you really don't have to run out and buy another heat pump.)

    Google "desuperheater," or ask your ground-source heat pump rep about desuperheaters.

    [Later edit: The advice I gave in this response was too categorical. To hear a different perspective, read the comment posted by John Clarke (comment #57, 4/24/2012 at 16:20) and the comment posted by Curt Kinder (comment #58, 4/24/2012 at 23:24).]

  44. ndZ4Zkw2u4 | | #44

    Not a bad product, just bad applications
    I installed an add-on Geyser HPWH in the finished basement of my older home in Central Virginia. It cost about the same as the commercial-grade dehumidifier that was recommended to me at the time, and has noticeably lowered our electric bills for hot water (installed 3 years ago) while keeping the basement cool and dry all summer long. I now switch to an on-demand gas system during the heating season (feeding the same storage tank - my original electric resistance heater) because I had to replace the gas boiler anyway.

    Just looking at energy savings for hot water, I believe the payback to be about 10 years (maybe less with tax rebate). Add in energy savings for (not) running a dehumidifier and the equipment cost of the dehumidifier, and I am way ahead. Yes, in winter there is some cooling (when I used it that way), but I heat my basement with wood, so that was not a big issue for me.

    Downsides are limited to noise (not a problem for me as it is in a utility space) and some space cooling in winter. I can also imagine some situations where additional humidification would be necessary in summer making it not a true replacement for the dehumidifier. Even in this case, it would significantly reduce the load, and extend the life of the equipment.

    A HPWH may not be a great fit for many new homes, but for the older houses that I have always lived in, it is a great alternative to running a dehumidifier all summer long, heating up the basement, then pumping that heat back out again with the A/C. "free" hot water is just the icing on the cake.

  45. semipro | | #45

    Other advantages of HPWHs
    We have the GE GeoSpring installed in a basement.
    I want to point out a few other things about these units that I think are advantageous.
    - Probably mentioned already, de-humidification of my basement.
    - Less fouling of the water heater by minerals. Our previous electric resistance WH was acting as softening systems. Minerals would form on the elements and then break off, collecting in the bottom of the tank. The GeoSpring heating coil surrounds the metal tank and operates at a much lower temp and should prevent minerals from filling the WH. Of course those minerals are now making there way into our HW plumbing now where they weren't before. (This may not be good).
    - There is an opportunity to utilize waste heat from electronics such as my fridge, wireless router, etc or other sources by dumping it into the space where the HPWH resides.
    - The HPWH filters the air in my basement.

  46. wjrobinson | | #46

    HPHW units have many less than ideal issues imo
    Expensive product, that may not save in many ways in Northern NY imo..

    Worthy discussion and needed though, thank you Martin and GBA

  47. wjrobinson | | #47

    Heat Pump Water Heaters may not have come of age
    Heat Pump Water Heaters IMO have not come of age for use here in the Adirondacks for homes the way we build them now.

    Martin. the information and lack of information leads me to the realistic conclusion that my customers should not consider this product.

    1 Water is very inexpensive and very abundant here in the Adirondacks.
    2 Hot water is very inexpensive compared to anyone's complete spreadsheet of living costs.
    3 They are not less expensive, they are more expensive.
    4 They are not less complicated, they are more complicated.
    5 Their manufacture and disposal are a larger burden on the planet not less.
    6 .....

    Still, this discussion is very good and very enlightening, soup for all.


  48. wjrobinson | | #48

    Repetitious post edited.

  49. wjrobinson | | #49

    an unnecessary gadget?

    Dana, good point, but you fail to mention other reasons not to buy one of these noisy, expensive, poor payback, water heaters. Seems like they are just the latest of "gadgets?"

  50. SJR333 | | #50

    Oil Fired Hot Water
    We recently purchased a house with a hot water heater connected to the boiler working as a zone. Does anyone know of a calculator or comparison chart which includes oil as a source?

    Could an HPHW be located in a 330cuft furnace room? The average temperature in that room is easily 5 degrees warmer than the rest of the house.

  51. smalld | | #51

    Solar Thermal Heating - Dismissed????
    Martin: in regards to your outright dismissal of Jasons' comment; Please visit and check it out, might be worth your while. While your at it feel free to contact Bill or one of the others at the sight, the reality might surprise you! Canadian companies, eh!

    Regards, smalld

  52. GBA Editor
    Martin Holladay | | #52

    Response to Steve Rust
    Q. "Does anyone know of a calculator or comparison chart which includes oil as a source?"

    A. Yes; there is such a table on this page published by the ACEEE: Water Heating. You'll notice that an oil-fired water heater has the highest life cycle cost (over 13 years) of any option on the list. The main reason for this is the high cost of oil. Needless to say, the cost to operate an indirect water heater like you have (a domestic hot water tank connected to a space-heating boiler) will differ from the cost to operate a stand-alone oil-fired water heater; but the chart is still useful.

    Q. "Could a HPWH be located in a 330 cu. ft. furnace room? The average temperature in that room is easily 5 degrees warmer than the rest of the house."

    A. Good question. The short answer is no -- because you would be violating the manufacturer's recommendations. (The room is too small.)

  53. GBA Editor
    Martin Holladay | | #53

    Response to Rhaud Macdonald
    You have provided a link to the web page of a distributor of solar thermal equipment. It doesn't surprise me at all that a company that sells such equipment claims that it's cost-effective to use solar thermal equipment to heat water or provide space heating. However, this does not constitute evidence or even useful analysis.

    No third-party researcher or academic team that I am aware of has found that a solar thermal system can heat domestic hot water cheaper than a water heater burning natural gas.

  54. icestationzebra | | #54

    solar thermal
    Hi Martin (and all),

    I am curious about the cost effectiveness of solar thermal hot water systems. You have been stating in some of these blogs about their cost have very long "payback". 1) Were you using the DOE comparisons chart that shows a 13 year life cycle cost compared to other hot water energy source systems? If so, I don't think that it is a fair comparison, since the big ticket hardware for solar hot water systems can last longer than 30 years. 2) Is it the solar storage tank that makes it the limiting factor in the solar hot water system lifecycle? 3) And are you including the currently available tax credits in the system cost? I appologize for having missed your source for that statement in any previous postings and asking you to restate the facts.

  55. icestationzebra | | #55

    HPWH using fridge heat
    I've been following the blog on using the HPWH to scavenge the fridge waste heat. What is the fan capability that is in the add on heat pump water heaters (Geyser & Airtap) regarding moving air in a 4" or 6" duct? I have a scenario where the existing 80 gallon electric hot water tank is directly below the refridgerator in the kitchen. The basement (a workshop - zone 5,) is currently heated with thermostatically controlled electric resistance fan convectors, so scavenging heat from them is not a good application during the heating season. The shop size is more than 2800 cu ft volume. The shop also requires dehumidification during the summer, so a hpwh is a good aplication for spring, summer, fall.
    If I could route the hpwh intake air from 4 feet above (the fridge) and dump the cool dehumidified air to the shop, perhaps the effective purchase cost & installation (homeowner) would be juistified for 3 season operation. Any thoughts?

  56. GBA Editor
    Martin Holladay | | #56

    More on solar thermal payback
    Aaron Becker,
    Here's a well-researched paper on solar thermal payback: Cost, Design and Performance of Solar Hot Water in Cold Climate Homes.

    The paper by researchers from Steven Winters Associates provides detailed monitoring data from two solar hot water systems. The respective simple payback periods for these two systems: 58 years and 76 years.

    Of course, rising prices for natural gas or electricity will shorten these payback periods. Incentive and rebate programs will also have the effect of shortening these payback periods.

  57. user-963068 | | #57

    RE: Martin's Response to Janet Bergman Wilkinson
    One thing I think you have to consider is the duty-cycle of the GSHP and how much hot water your desuperheater will actually produce. If the GSHP is running on a daily basis year round then your argument against the HPWH makes sense. In a case where the GSHP is not operating continuously (such as in our high efficiency house) then the desuperheater doesn't help unless you have a huge storage tank. After much research and discussion as well as the lack of natural gas for our site, we chose to pair the AO Smith HPWH with our GSHP desuperheater. The installation is in a conditioned basement, part of which is living space and I can attest to the noise of the unit. We plan on sound-proofing the mechanical room in the near future since it does have the GSHP, HPWH, ERV, and the obligatory wastewater lift station (below grade bath).

    We have been in the house for less than a month so I can't attest to the cost effectiveness but we have been operating it in efficiency mode to avoid using the resistance heaters. There are only two of us living in the house so we don't have the issue of regeneration times but on days when the desuperheater is operating we expect it to reduce the regen time significantly. Again, our GSHP is very low duty-cycle at this time of year so no empirical data to back up our designed efficiency.

    We also have a 40 gallon storage tank (resistance water heater w/o electricity connected) for the desuperheater which feeds the HPWH and therefore our 60 gallon HPWH effectively has 100 gallons of hot water (when the GSHP is operating).

    Your comment on the need for the condensate pump is well advised. We piped the condensate out to be added to our rainwater collection tanks (as opposed to adding it to our septic system). A little mentioned advantage is that the basement humidity is reduced while the HPWH is operating which is generally a good thing. No more need for that dehumidifier (which was noisy, generated lots of hot air, and required emptying or a condensate pump attached). I wouldn't suggest that as a reason to buy a HPWH but it does provide an added benefit to us.

  58. watercop | | #58

    Response to several
    I agree with the point made that just because heating degree days are based on 65*F doesn't mean houses start needing heat at 64*. When I lived in Mass we didn't reach for ther thermostat until outdoor temps dipped into the 40s.

    An attic can be a great place for extra heat to pull into a HPWH at very favorable COP factors, but make sure the weight of the HPWH is well supported and that proper provision is made for both condensate water and possible plumbing leaks.

    I have EXACTLY what Martin H tells Janet NOT to combine...My WaterFurnace geo-sourced heat pump has the desuperheater option that warms water in an 80 gallon preheat tank. The preheat tank supplies a second 80 gallon tank heated by a Geyser HPWH. The result is water heating costs no more than $15 per month, and often less than $5 for a family of 4-5.

    During summer and what passes for winter in north Florida, the Geyser runs little since water leaving the preheat tank is 100-130*F. During spring and fall, the Geyser carries most of the load since there is little HVAC load. The Geyser's dehumidification is a nifty added bonus.

    If I rebuilt the system today I'd use a 60-80 gallon integrated HPWH rather then the Geyser, since the integrated units are now less expensive, quieter, and more efficient than a Geyser heating a separate tank.

    An HPWH can be installed in a smaller room warmed by a furnace. A 70 page study of GE HPWH by Advanced Energy in North Carolina extensively tested a small room installation. The GE kept most of its efficiency even as the room dropped to 55*F.

    I am concerned that overcooling a small room with an HPWH in a humid climate could lead to dew and mold formation within the walls of a small room cooled to 55*F by an HPWH. The Advanced Energy HPWH study did not address that concern

  59. GBA Editor
    Martin Holladay | | #59

    Response to John Clarke and Curt Kinder
    John and Curt,
    I stand corrected. Thanks to both of you for sharing information on your experiences combining a ground-source desuperheater with an air-source HPWH. I learn something every day.

  60. lutro | | #60

    Please check my analysis of
    Please check my analysis of the heat flow relating to HPWH systems discussed in this article. Heat pumps move heat energy from one place to another. When the heat pump is installed inside the conditioned living space, the energy being moved into the hot water can only come from a) the outside world (solar input and heat conduction from the earth or outside air into the living space), or b) energy introduced into the home via electricity or fuel. In a heating situation, all the calculated advantage of the heat pump, either EF or COP, comes from heat that is already in the house, having been purchased, in case b), or "donated" by the environment, in case a). The heat transferred to the domestic hot water is being removed from the living space, and that heat must be replaced.

    While a homeowner might not mind a slightly cooler basement, or might not notice the impact of an air to water heat pump on their space heating needs, this doesn't change the fact that all the heat moved by a HPWH is being taken from the living space. Does this not mean that the true EF or COP is roughly 1, regardless of the industry calculation standards which provide much more attractive numbers?

    In a cooling situation, heat is moved from the living space, where it isn't wanted, to hot water, where it is. I can see the energy efficiency advantages there, plus the dehumidifying that has been discussed. But for heating, unless the HPWH is drawing heat from the building that would otherwise be lost, then I don't see how it can have a genuine energy advantage.

  61. GBA Editor
    Martin Holladay | | #61

    Response to Derek Roff
    Thanks for your comments. I will add two more situations that you didn't address fully:

    1. In a heating climate, a HPWH located in a garage does not steal space heat from the house.

    2. If the HPWH is located in a basement that is ordinarily hot (because of the presence of an inefficient boiler, an inefficient furnace, or uninsulated ductwork) and rarely visited, the lowering of the basement's temperature will not necessarily result in the need to burn more space-heating fuel.

  62. lutro | | #62

    Still wanting to clarify
    Thanks for your response, Martin. I'm still hoping to understand more fully. In you point 1, if the garage is not heated space, then I agree that HPWH wouldn't impact the heating loads appreciably. But did you not say that an HPWH should be in a room with an ambient temperature of at least 50 degrees F, preferably more? I would imagine that an unheated garage in many heating climates would be below this temperature during some or all of each day for a good percentage of the year.

    On your point 2, in a basement that is ordinarily hot, either that heat is being transferred to the living space, or it is being lost to the outside environment. I would hope for more of the former than the latter, but no doubt cases vary. As I mentioned, it seems to me that except to the extent that it uses heat that would otherwise be lost, an HPWH inside conditioned space is using heat that would otherwise contribute to warming the house. What would you imagine is an average amount of heat lost to the outside world in a hot basement of the type that you describe?

  63. wjrobinson | | #63

    Martin, even in your too warm
    Martin, even in your too warm cellar the too warm cellar is aiding heating the home above it. And same for cooling an attached garage. The separation wall being cooler will make the home use more energy.

    Basically the idea works as a secondary heat redistributer at the added cost of buying and running a HPHW gadget.

    For cooling climates a noise free unit in the home or attic or garage makes much more sense.

    Lastly as I have said, heating water is the least expense any of us pay. An easy way to cut the expense is to simply use less heated water. Small tanks that run out of water save and require no fancy added gadgetry.

  64. GBA Editor
    Martin Holladay | | #64

    Response to Derek Roff
    I understand your basic point about the physics involved. You're right -- lowering the temperature of a basement will probably require the furnace or boiler to work a little harder. The question is, "How much harder?"

    To illustrate my point, let's take an exaggerated example. Imagine a house with two big rooms. One is an occupied room that stays at 70 degrees. The other room is an unoccupied room that also stays at 70 degrees. The occupants never enter the second room.

    If you put a HPWH in the second room, the HPWH might lower the temperature of the room to 60 degrees. It's hard to say whether the home's furnace is working any harder at this point; the temperature of the air has been lowered, and the space heat has been transferred to the water in the water heater. But maintaining the second room at 60 degrees may not take any more heat from the furnace than before the HPWH was installed. You could argue that the comfort in the home has been degraded, because one room is now cooler (a fact that normally -- in the absence of a HPWH -- would lead one to guess that the furnace is burning LESS fuel, not MORE fuel -- all other factors being equal). However, comfort is not an issue -- because the occupants never enter the second room.

  65. GBA Editor
    Martin Holladay | | #65

    Response to AJ
    1. The heat added to a home by a refrigerator (or any electrical appliance located inside the home's thermal envelope) while it is operating is equal to the current drawn by the appliance. If the refrigerator draws 300 watts, then it adds 1,024 Btu/h to the home when it is operating.

    2. All other factors being equal, lowering the temperature of one of the rooms in your house during the winter months will result in energy savings. Maintaining a basement at 60 degrees for 4 months requires less space heating energy than maintaining a basement at 70 degrees for 4 months. If the difference in fuel use between maintaining a basement at 60 degrees and 70 degrees is X gallons of fuel oil with a heat energy value of Y, and that energy is transferred to a tank of water, the net result could be a wash in terms of space heating energy use.

    That said, in the real world, it is much more likely that installing a HPWH in a basement will, in fact, require the furnace to work a little harder. As I said earlier, the real question is, "How much harder?"

  66. 634LbPYnie | | #66

    From a newbie
    This has been a great discussion and the one that got me to join. I'm a newbie but have wanted to add either PV or solar thermal for quite a while. I live in Birmingham, AL and my natural gas DHW heater just bit the dust. I have been considering natural gas tankless heaters, but after reading this discussion I am thinking that electric is the way to go assuming that PV is in my near future. Martin, you said standard electric resistance tank heaters powered by PV are likely to be more efficient than solar thermal, but would that be true of electric tankless heaters as well? Your last blog doesn't really make me want to go tankless but what about smaller, point- of-use units? Is the payback time just terrible?

    I also agree with the comment about reducing fossil fuel use. I'm willing to pay a bit more initially if I can reduce a) natural gas consumption now and b) grid electric later when I install PV. Our electricity is made from "clean coal"--an oxymoron if there ever was one.

    Thanks for the great topic!
    Edwin Booth

  67. GBA Editor
    Martin Holladay | | #67

    Response to Edwin Booth
    Q. "Martin, you said standard electric resistance tank heaters powered by PV are likely to be more efficient than solar thermal."

    A. I think you misunderstood. My point concerned cost-effectiveness, not efficiency.

    Q. "Would that be true of electric tankless heaters as well?"

    A. The efficiency of electric tankless water heaters is a little higher than the efficiency of electric-resistance tank-style heaters. Electric tankless water heaters have an EF of about 0.99, while electric-resistance tank-style heaters have an EF of about 0.90 to 0.93.

    Q. "What about smaller, point-of-use units? Is the payback time just terrible?"

    A. Point-of-use electric water heaters make sense for some applications. (For more information on this topic, see All About Water Heaters.) When you ask about payback time, I'm not sure what you mean. The first question you have to clarify is, "Compared to what?" All payback calculations depend on local energy costs, so I probably can't help you; you'll have to research local energy costs and the cost of the equipment and do the math yourself.

    For more information on payback, see Payback Calculations for Energy-Efficiency Improvements.

  68. wjrobinson | | #68

    Martin, physics or magic?
    Martin, physics or magic? Moving home heat to water then draining the water out of the home is physics. The heat is gone and will be replaced by the heat system that it was taken from. You also know that the delta T across a wall or floor matters but not for HWHP for some magical reason.

    You even mentioned refrigerator adding heat to a home. It only adds the net heat waste from the light bulbs and motor inefficiency not the warmth of the coils which is equaled by the cold of the inside coils.

    These are worthy discussions but let's stick to physics.

    Edit; OK.. even more clear, I agree all the work done by the refrigerator motor is inside the home so yes the watts used converted to btus is the added heat. What I was trying to say is that your average Joe or MaryAnn may think the warm coils on the backside of the refrigerator are the source of net heat gain, while disregarding the cold coils effect. Anyway, we agree about the btus added. Where we will remain apart is the idea that cooling a cellar does not effect the home above. It has to. You with your I=B+R which uses delta T in calculations know that if a delta T is 5 degrees more, the equation will show more btus needed. And so the furnace will be providing the added btus and those added btus are what heat the water in the HPHW gadget.

    More thoughts on your 2nd point Martin. If I lower the temperature of any internal part of my home by dumping that heat outside the home continuously, like leaving a window open or running a HWHP that dumps the heat into the water that I dump outside the home, I am effectively removing heat that I paid for and came from my HVAC. And the adjoining partition being colder sets up a delta T that will take more btus than if there were no open window or HWHP. You are close to inventing perpetual heat.

    We shall remain in partial harmony as usual. Enjoying the physics.

  69. user-444644 | | #69

    Response to Stan Smith
    With such high performance mini-split technology/equipment availible for forced air systems, I was confused as to why all the HPWH's in the U.S. have indoor evaporators. Trolling the internet a few months ago, it was a delight to discover that there are mini-split type water heaters available somewhere in the world. It is great to have you chime in on your experiences with one and providing some hard numbers (prices, temperatures...) The links you provided confirmed my suspicion that they are built with Asian parts (Toshiba outdoor unit) I'm looking to heat some radiant floors with in and if I could buy a HPWH here in the U.S. for $4500 that would work down to 23F I would do it tomorrow.
    thanks for your input.

  70. user-304075 | | #70

    New home water heating decisions

    I am designing a passive solar house to be built slightly north of Seattle. I will use SIPs to super insulate and seal the house. Triple glazing from Cardinal glass will provide solar gain.
    One of my last decisions is how to provide hot water for the home. Gas is not avaiable but electricity is. A large amont of thermal mass will store the solar heat gained and I anticipate low heating needs; so the home will not need for a large heater than can produce hot water for heating and other uses.

    I am not convinced that solar water heaters are cost effective.

    The home is modest at 1825 sq feet and will only have two occupants with what is probably a lower than average hot water usage. We only use cold water in the washing machine.

    I have read three of your recent posts on heating water: All about water heaters, Are tankless heaters a waste of money and this post.

    Based on your posts I am currently thinking to add a large uninsulated water tank inside the house that will settle to the average house temperature of ~68 degrees. This will also add thermal mass. Then I will use three point of use devices such as the Stiebel Eltron Mini units. One under the kitchen sink and one near each of the two showers. Under the showers I would install heat recovery devices to ensure the temperature can get hot enough.

    I would appreciate comments on this scheme

  71. GBA Editor
    Martin Holladay | | #71

    Response to Stephen Carlton
    Your plan for water heating sounds fine to me.

    My only comment: just because you specify SIPs, doesn't mean that your house is superinsulated.

  72. user-304075 | | #72

    Water heating strategy for Passive House
    I am just completing the design of a home which I will build next year close the the border with Canada north of Seattle. The climate is moderate/marine.

    I am using a passive house strategy. The house is 1825 sq ft and uses SIPs to provide high insulation values and sealing. Triple glazing from Cardinal will be used to maximize solar gain. High thermal mass will be built into the slab and be well coupled to the heat gained. A heat recovery ventilator will be used. I estimate my heating needs to be quite low and I am not designing in a large heater than can produce hot water for the house as well.

    Two people will live in the house so hot water demand will be modest, we only use cold water in the washing machine and hot water is not used to heat the house.

    I believe solar hot water systems, especially at this loactio, are not cost effective compared to other methods.

    Based on recent posts on this blog about point of use water heaters, tankless heaters and heat pump water heaters I have come up with the following scheme. I should point out that I believe simple is best and I hate waiting minutes for hot water to arrive at a faucet or showerhead.

    I plan to place a large uninsulated water talk inside the home so that it is heated to the homes ambient temperature of ~68 degrees by the solar gain. This will also add to the thermal mass in the home. I will distribute this warm water to three point of use heaters such as the Stiebel Eltron Mini™ Series. One at the kitchen sink and one at each bathroom near the shower. Under the shower I will use heat recovery devices in the drains.

    I would appreciate comments as to the scheme and I will use them the modify and finalize the house design.

  73. user-304075 | | #73

    Double post

    Sorry for the double post, I hadn't realized that my post was up and that you had responded.

    I understand that SIPs don't equal super-insulated. I started down a passivhaus path but now am following your recommendations on insulation, especially given that my house will be in a fairly moderate climate. I will post some other questions about insulation and the way I use it on the appropriate blog post.

  74. Alan Abrams | | #74

    hpwh as a dehumidifier
    Hi Martin and fellow readers--

    in a current project in a mixed humid climate, we will be adding a two story addition with new basement, to an existing 2 story masonry and frame house on an existing, partially finished basement. we plan to condition the new space with a multi zone heat pump. the existing house will remain heated by a boiler radiator system, and will be cooled by an ingenious but marginal AC system with air handler in the attic.

    to get to the point of the issue, the existing AC system is inadequate to prevent mold growth in the existing basement in summer time. since the project will include a new water heater--does it make sense to consider a HPWH located in the existing basement, not only to provide hot water, but also to provide dehumidification in that area? It would require some through-wall fans of course, to accomplish this.

    alternately, the new heat pump could include an additional zone to condition the existing basement. but the assumption here is that when you add the dehumidification capability of the HWHP into the efficiency calculation, it might cancel out any other disadvantages, including higher first costs for the equipment.


    Alan Abrams - Takoma Park, MD

  75. GBA Editor
    Martin Holladay | | #75

    Response to Alan Abrams
    My recommendation would be to first try to figure out why you have a mold problem in your existing basement, and if possible to address the moisture problem with something other than dehumidification.

    Possible causes of your mold problem include air leaks that introduce humid outdoor air, damp soil around the foundation, or a clogged footing drain.

  76. G3u9q43A2c | | #76

    heat pumps
    Heat Pumps new technology can assure a ROI in a2 years depending on installation and climate conditions.
    In Europe the new frontier is the application of multifunctional all-in-one heat pumps, those units can provide cooling, space heating and hot domestic water with a great saving.
    For additional information write me at [email protected]

  77. rustyshackleford | | #77

    heat pump noise
    I am a DIY homeowner, adding a room that requires me to move my direct-vent gas water heater. (It's a State one that has performed flawlessly for 25 (sic) years, but I'm assured it'll start leaking if it's moved, so time for a new one).

    Been looking at the bewildering variety of water heaters available to day, and am now convinced that heat-pump style is right for me. I'll add a wrinkle I haven't seen in these comments: my space heat is extremely cheap and PC, since the dual-fuel heat-pump only comes on if the passive solar and catalytic woodstove haven't kept up. So if I put it inside, the HPWH would be using cheap heat in the winter and helping to cool the house in the southern summer. A huge win.

    One big fly in the ointment - the noise. Sounds like these things are pretty loud and my house ain't that big. I can locate it pretty far from both bedrooms, but sounds like it's loud enough that even being fairly close to the living room and the study will get annoying. I guess there's no way out of this, since of course it can't be sealed up in a closet. Putting it in the crawlspace might be nice, since I have a serious humidity problem and am converting to a sealed crawlspace. But the most clearance I have down there is 4ft, so I guess that's a no-go too; too bad someone doesn't make a lowboy style HPWH.

  78. GBA Editor
    Martin Holladay | | #78

    Reply to John Eyles
    Once it is installed and operating, report back here -- let us know how loud it is.

  79. rustyshackleford | | #79

    I'm thinking I'm not gonna
    I'm thinking I'm NOT gonna install one - the noise is a deal killer. Too bad someone can't come up with a noise cancellation system: like noise-cancelling headphones, except a loudspeaker that cancels the compressor/fan nose.

    I'm thinking ERWH is the way to go for me. Just talked to energy-expert buddy, who said utility companies are hoping to get a lot of people on the plan where they can control your ERWH remotely; thus millions of people's ERWH's will effectively become a giant "battery" - when there's spare generating capacity (esp. for inconsistent renewables like solar), that excess energy can be put into people's water heater tanks. Pretty neato ! It's also clearly cheaper for me (than propane) and there is a path to PC-ness by adding PV solar.

  80. GBA Editor
    Martin Holladay | | #80

    Response to John Eyles
    You had me confused there for a while -- ERWH? -- until I guessed that you are probably talking about an "electric resistance water heater."

  81. rustyshackleford | | #81

    Yessir. With all the lingo
    Yessir. With all the lingo from the insiders here, I figured no problem using such acronyms ... :-)

    I need to figure out if my electrical service can handle adding that huge electrical load though. Though I am an electrical engineer, I'm not quite sure how. Two issues I suppose - is there space for a double/240v breaker, and is the wiring from the transformer up to that many total amps ? Anyone know of a link to help me with that ?

  82. GBA Editor
    Martin Holladay | | #82

    Response to John Eyles
    The electrical load will only be "huge" if you install a tankless water heater. If you install an electric resistance water heater with a tank -- by far the most common type -- the electrical load is not particularly huge.

    In any case, if you are "not quite sure" how to determine whether your existing service can handle any extra electrical load, then you're reached the limit of free Web advice. It's time to call an electrician.

  83. rustyshackleford | | #83

    Yes, I guess 20 amps isn't
    Yes, I guess 20 amps isn't really "huge" - assuming it's true only one of the 4500 watt elements is energized at any given time. Interestingly, if you look at the spec sheet for the AO Smith ERWH's, it says 4500/6000 watts. I called and asked what that meant and they said the 6000 watt was a special order. Never heard of that before.

  84. djowhite | | #84

    HPWH for coastal Massachusetts?
    Lots of good discussion on here, glad I found this forum. Like one or two others here, I've been thinking for a while about whether a HPWH would be a good solution just for the summer months. We have an oil furnace for both heating and water, but during the summer its really only used for hot water. I'm now looking at $750 for a tank of oil and there's only one direction that price is going in the future! Would it make any kind of economic sense to install a HPWH, shut the furnace off for the summer and just use the HPWH, shut the HPWH off for the rest of the year and then just rely on the furnace? Has anyone actually tried this?

  85. GBA Editor
    Martin Holladay | | #85

    Response to David White
    First of all, the space-heating appliance in your basement is a boiler, not a furnace.

    Second, you are quite correct that using an oil-fired boiler to create domestic hot water in the summer is extremely expensive. If you have somewhere to put a heat-pump water heater (a basement with a high ceiling, for example), the HPWH will cost far less to run. The HPWH will also help to cool and dehumidify your basement.

    The only disadvantage to this approach is the high cost of the equipment and the relatively long payback period. If the high cost scares you, you might consider installing a conventional electric-resistance water heater for use during the summer months. In either case, you can lower your electric bill by investing in a PV system; I hear that Massachusetts has some good incentives.

  86. djowhite | | #86

    Thanks Martin
    Thanks for the advice Martin - and correcting me on what I have. Growing up in Britain, we always called it a boiler. In the US, I've only ever heard it called a furnace. I thought we were just using different words for the same thing - two countries separated by a common language etc. We have space to put a HPWH right next to the boiler and I've always assumed that would make the plumbing easier. I'll look into it further, thanks again.

  87. flatusm | | #87

    Excellent time to buy
    My 20 year old heater finally burst a month ago and it turned out good karma which led me to the Geospring. There will never be a better time to go to a hybrid water heater.
    Apparently, the 2009-2012 blue Gen 1 models were sloppily made in China of substandard plastic and coils that actually corroded each other when wet. The new red-topped Gen 2 ones are made in Kentucky using state of the art techniques, and much upgraded parts. The bad reviews from the old units lowered the price from $1599 to $1199. Until 5/29, it was on sale at Lowes for $999 with an instant $200 rebate, thus $799. With the Fed tax break of $300 and a Puget Power refund of $500, my cost was $-1. Well, I had to pay sales tax and a few bucks for a condensate hose.
    The Regime (DOE) is mandating new water heater specs that can only be met by Hybrids as of 2015. Expect all the rebates and discounts to vanish after that. Eventually, element heated units will go the way of the incandescent bulb.
    Fortunately, however, the higher total unit cost means the tank itself will be better made; this one is a 10 year ($500 equivalent standard heater) vs. a 6 year ($350 standard heater) tank. As to the heat pump longevity, well, it is pretty much the same as the one in the 25 year old almond fridge you probably still have running in your garage. I think GE likely overbuilt these Gen 2 ones because of the chinese fiasco. The new single fan is quiet, unobtrusive white noise, too.
    I did a few things to maximize my benefits. I raised the heater about a foot and made sure there was more than 7" clearance all around for airflow. This allows it to draw air from the hotter air near the ceiling, and gave me better drain options. I will have to punch a small hole in the ceiling to change the anode, oh well.
    It is in an unheated but insulated room behind the garage that never freezes due to mild Seattle weather and the washer/dryer on the other side of the wall providing heat that will now be recycled. The room is about 8x14, and the cooling effect is comparable to a compact window AC unit--which is in line with the 700 watt heat pump draw. I am setting it to 140 to get through four showers nightly.
    I think if you consider airflow and heat transfer you can get a lot of advantage out of these units. There is no question that moving heat is cheaper than generating it. But there has to be a gradient within the compressor's rating. In this case, I think 55+ degrees f. ambient air (specs say 45 to 120) is the best operating range. Below 55, it will struggle to keep up and you will set it to use the elements.
    What makes me especially happy is that it is near my hot tub room and 'conservatory'. There is plenty of waste heat I can duct from both places, and the dehumidification is an extra bonus. It pulls a gallon a day from the air.
    The one downside is GE is recalcitrant thus far with providing technical data and parts for DIY repair. So, it will be a $400 service call if it breaks. Again, though, I personally use an air conditioner from 1982 in the aforementioned hot tub room, and it has never been serviced. The hardware on this water heater looks very well designed and built. I'm sure the fan and even compressor are shelf parts you could look up, but doubt anything will break in a ten-twenty year timeframe.
    Sorry to be so long winded, I just wanted to summarize all my own research.

  88. LarryCroome | | #88

    Appreciated the read
    This topic is still up in the air just like our precious energy dollars. Heat pumps in fact are a little like magic in terms of capitalizing on the phase change of refrigerant and locating the heat loss or gain in the right place. There is a substantial market future for heat pump hot water tanks -ONLY if designers and builders are ready to shape their whole building philosophy around ALWAYS incorporating the synergies of our cooling and heating needs. This can bed more simple than complicated -ONLY with the correct advance design of spacial needs and mechanical. I am building a net Zero home in Canada with R40 walls and roof plus solar mass concrete /insulated foundation. It will be a mechanical process in the works over the next while after the basics are installed. I have been planning the heat pump hot water from day one after calculating all other costs of achieving hot water. The intake to the heat pump will be from warm sun collected -when the sun is shining, warm fireplace air when the fire is burning, and the rest of the time from interior air. The fridge is located with its back to the mechanical room and plan on putting a 'cold-sinc' at the fridge coils as well as the master bedroom shower upstairs will have a drain wrap for warming the cold water into the hot water tank. ETC.
    If you build your home efficiently enough... as I am, then domestic hot water is by far the most costly energy -then the cost of ventilation air and then space heating. We will capitalize on passive solar when possible and have 2, 3 and 4 pane windows used. I have a long list of synergistic design elements with some costing near ZERO. Our Electric will be PV and feed back to grid. Later we may put in a small bank of batteries. Electric company is charging $0.105 per kwhr and paying $0.10. That number will only be going up --for BOTH. The home design is such that the pv panel install is easy to go in and easy to keep clean.

  89. Stixoffire | | #89

    I thought about simply ducting to and from the Attic - in the south and especially in an older home - cooling the attic a little from its normal 140 plus temp is not a bad idea. I have an Aquatherm heating system in Orlando that is run by Natural Gas - they slam the Gas price in the winter so I am not sure if I am saving anything or not. But I can imagine how well ducting to the Attic would be 9 months out of the year. If the attic is cooler the house can be cooled and kept cool cheaper - but then again how much cooler would that attic be considering the Water heater should not be on 24 /7 or even close to that. Of course seems to me just running pipes back and forth through the attic should keep the water hot and its free most of the year.

  90. GBA Editor
    Martin Holladay | | #90

    Response to Ken S
    Your attic air temperature should be irrelevant to your energy bills or your comfort, as long as your attic floor is adequately insulated, and as long as you don't have any ducts up there.

    If you have ducts in an unconditioned attic, you have a problem. But your suggested remedy is definitely not the most logical way to solve that problem (ducts in the attic).

    Attempts to save energy by blowing air from the vicinity of a heat-pump water heater to a different location usually don't work, for four reasons:

    1. The cost to install the duct and run the fan are more than any energy savings;

    2. Homeowners who install these systems usually haven't considered the question of where the makeup air comes from;

    3. It's hard to prevent air leakage through the duct (and through your thermal envelope) when the fan isn't operating; and

    4. It's hard to choose and program a control system so that this Rube Goldberg fan is only running when you want it to.

  91. sporder | | #91

    HPHW in Rhode Island
    We just installed a GE Geospring in our basement in Providence. The house is undergoing an energy retrofit - R60 roof, r30 walls, r20 basement walls. The basement is currently unheated. Leaving aside for a moment that the product was defective upon installation (a common problem with the geospring), we did this because there is a $750 rebate in RI for this unit, making it a $350 gamble. In contrast, the Steibl unit would cost $1800 after rebate, and is too tall to fit in our basement anyway. So, for the green building gurus, assuming we can get it to work, is a $350 Geospring worth it, or should we just get a natural gas heater ? We are a family of three, and although one of us will be a teenager soon, our hot water use isn't all that much at the moment.

  92. GBA Editor
    Martin Holladay | | #92

    Response to Stephen Porder
    This article explains the type of house (and family) for which a heat-pump water heater might make sense. These appliances aren't for everybody. If you are uncertain about whether it makes sense for you, I suggest that you re-read the article.

    Q. "Assuming we can get it to work, is a $350 Geospring worth it?"

    A. That question is easy to answer. Yes, it is worth it. That's a great price. However, just because it's a great price doesn't mean that it's best for your house and your family.

    Q. "Should we just get a natural gas heater?"

    A. If you have already installed the Geospring, and if the Geospring has a warranty, I wouldn't give up on it just yet. Use it for a year and decide whether it meets your family's needs.

  93. tankhacksaw | | #93

    Does anyone know what's going on with the company?

  94. GBA Editor
    Martin Holladay | | #94

    Response to Greg Coleman
    There was some discussion about the company on an earlier Q&A thread.

    According to True South, "The manufacturer is no longer warrantying the units."

    According to Dana Dorsett, "It's a relatively small start-up company that got into it without the deep manufacturing & support experience of a big player like GE or AO Smith. I hope they continue to survive as a company."

  95. grepucci | | #95

    Response to Cartlund Monson; et al
    Where did you get the data on the updated Geospring units? I continue to see current reviews/comments online (up to December 2015) which reference recently installed units that:
    1. still have problems with incorrectly installed anodes which leak at first pressurization
    2. have developed leaks on units purchased in 2013 (after the 1st Gen fiasco)

    To all:
    It seems unfortunate that there's not as much activity/follow-up on this blog as there was during the first year of activity - there's alot of great information here, which would be improved by continued data on HPWH usage.
    I'm looking to replace an old fashioned resistance water heater with a newer HPWH, the only difficulty is determining reliability data for the ones out there that have been updated to comply with the 2015 regulation changes. My current unit is in the garage, and Arizona provides plenty of hot air :) during most of the year to make this a worthwhile installation.

    Of some concern is the fact that we just recently installed a soft water system, which, from what I've read, will have detrimental effects on the anode of the unit in the short term. I'd prefer to install a powered anode to offset that problem, but haven't seen any information on whether that's possible in these HPWHs. Any information about that would be appreciated.

  96. qcoder | | #96

    WiFi monitoring
    Anyone know what hoops have to be jumped through to put a GE Geospring GEH50DFEJSRB on our home local WiFi network? There's a $35 GE module you can buy, but all it does is (apparently) make the device available from a Smart Phone.

  97. Brian Knight | | #97

    Rheem's Prestige challenges opening sentence
    Great article and comments. Rheem's new Prestige offering advertises UEFs of 3.55 for 50g and 3.7 for 65 and 80g models. This seems to make natural gas more expensive than electricity in most markets, especially when using updated UEF ratings of gas model comparisons. Maybe there was an update since this was written but Steibel Eltron advertises a 3.39 EF, not 2.51.

    Yes the modeling is complex for colder climates but it now seems opening statement no longer holds up in majority of utility markets. Cautiously optimistic is a great term for this new entry.

  98. GBA Editor
    Martin Holladay | | #98

    Response to Brian Knight
    Thanks for your comments. It might be time for a new article on the topic of heat-pump water heaters, in light of continuing technical improvements.
    [Later edit: The article you requested has been published. Here is the link: "Revisiting Heat-Pump Water Heaters."]

  99. user-626934 | | #99

    New article
    Yes, please! Most of the manufacturers are on their 4th or 5th generation of HPWH design. Perhaps you can release it in tandem with “Solar hot water is really really really dead”. ;-)

  100. GBA Editor
    Martin Holladay | | #100

    Response to John Semmelhack
    You made me smile.

    I've been itching to write the "really really really dead" article!

  101. midnightengineer | | #101

    I purchased a GE Geospring HPWH in 2011. I bought mine online for $1250 shipped to my house and installed it myself. Took me an hour using stainless braided water hoses and Sharkbite fittings from Lowes. 12 months later the condenser coil leaked and was replaced under warranty at no cost. Repair tech said he had replaced hundreds of them but the replacement coil was from a different supplier. It's now 2018 with no further issues. Saves me ~ $40 per month on my power bill in Florida operating in hybrid mode and keeps my garage noticeably cooler. I'm extremely pleased.

Log in or become a member to post a comment.



Recent Questions and Replies

  • |
  • |
  • |
  • |