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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

Posted on Apr 13 2012 by Martin Holladay

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 pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source 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 pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. 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. This feature improves the performance of the unit but introduces an energy penalty.

Most heat-pump water heaters have controls that allow a homeowner to choose one of three modes of operation:

  • Heat-pump-only mode (a mode that is energy-efficient, but that doesn’t allow long showers).
  • Hybrid mode (heat-pump operation plus electric resistance backup).
  • Electric-resistance-only mode (a mode that you could choose during cold weather, when you might not want the appliance to cool the space where it is located).

Heat-pump water heaters are clearly more efficient than electric resistance water heaters. Possible side benefits include dehumidification of the room where the unit is located, and space cooling (a side effect which is beneficial in hot weather but potentially problematic during the winter).

Measuring the efficiency of electric water heaters

Electric water heaters (both electric-resistance water heaters and heat-pump water heaters) are rated with an Energy Factor (EF) that is based on a standardized laboratory test procedure. The EF rating is the ratio of the energy delivered to the water divided by the energy used by the water heater. An EF test takes 24 hours; the testing standard specifies the volume and spacing of the hot water draws, as well as the temperature of the hot water and the ambient temperature of the room. An EF rating takes into account standby losses but not distribution (piping) losses.

A typical EF for a heat-pump water heater ranges from 2.0 to 2.5, while a typical EF for an electric-resistance water heater is 0.9. (The EF of an electric resistance water heater is always less than 1.0, due to standby losses through the tank insulation and at the pipe connections.)

While a unit’s EF must be measured in a laboratory, researchers can calculate a water heater’s coefficient of performance (COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. ) in any location where the unit is installed, as long as the proper monitoring equipment is in place. While the EF of an appliance is fixed, the COP of an installed water heater will vary, depending on the ambient temperature of the room where it is installed and the water use habits of the family using the water heater.

A heat-pump water heater with a COP of 1.8 is twice as efficient as an electric-resistance water heater with a COP of 0.9.

Factors that affect performance

A recent pilot study by researchers from Steven Winters Associates monitored the performance of 14 heat-pump water heaters installed in the basements of 14 homes in Massachusetts and Rhode Island. The study was sponsored by three electric utilities: National Grid, NSTAR, and Cape Light Compact. Robb Aldrich presented the results of the study on March 7, 2012 at the NESEANorth East Sustainable Energy Association. A regional membership organization promoting sustainable energy solutions. NESEA is committed to advancing three core elements: sustainable solutions, proven results and cutting-edge development in the field. States included in this region stretch from Maine to Maryland. Building Energy 12 conference in Boston.

The monitored water heaters included ten GE GeoSpring units, two A.O. Smith Voltex units, and two Stiebel Eltron Accelera 300 units. The water heaters were installed in older existing homes, not new high-performance homes.

The cost to operate a heat-pump water heater is hard to predict, because performance depends on the ambient temperatures of the room where it is located and the percentage of time that the electric resistance element is on.

The researchers identified the following factors that affect the performance and efficiency of heat-pump water heaters:

  • The higher the ambient temperature in the room where the unit is located, the better its performance and the better its energy efficiency. A unit that might perform at a COP of 2.35 at 68°F will only perform at a COP of 1.8 at 50°F.
  • The units installed in homes that used a lot of hot water (up to a point) had a higher COP than those installed in low-use homes. “If you don’t use much hot water, your COP is low due to the standby losses,” said Aldrich. “If you use more, the standby losses are smaller, so the COP is higher.”
  • Large volume draws of hot water cause the electric-resistance elements to kick in, thereby lowering the COP. “Concentrated draws of hot water make it hard for the heat pump to keep up,” said Aldrich. “A larger tank or a hotter tank might solve this problem.”

Energy use monitoring data

The measured performance of the 14 heat-pump water heaters enrolled in the study was fairly good. On average, the monitored COP was 1.9 — meaning that the units were more than twice as efficient as an electric-resistance water heater operating at a COP of 0.9.

The best-performing unit (located in a warm basement) had an average COP of 2.6, while the worst-performing unit (located in a small room in a very cold basement) had an average COP of only 1.0.

Where would I put a heat-pump water heater?

There are three places where you might put a heat-pump water heater:

  • If you live in a warm climate and you have an attached garage, put it in the garage.
  • If you don’t have an attached garage or you live in a cold climate, put it in the basement.
  • If you don’t have an attached garage or a basement, put it in a utility room — as long as the utility room is big enough.

It’s important to note that these three locations aren’t equivalent, and the performance of the heat-pump water heater will vary depending on the conditions of the room where it is installed. Many homes don’t have a good place to put a heat-pump water heater.

Before you can install a heat-pump water heater, you need to be sure that you can fulfill all of these requirements:

  • You need a room that is big enough; most heat-pump water heater manufacturers advise that the room should measure at least 750 or 1,000 cubic feet, although at least one manufacturer allows its unit to be installed in a room measuring only 500 cubic feet. Remember, in a small room, performance will suffer.
  • Ideally, the room will stay above 50°F all year long; however, if the temperature dips lower occasionally, your water heater will still work, although its efficiency will drop.
  • The room’s ceiling must be high enough to accommodate the water heater. Heat-pump water heaters are taller than electric-resistance water heaters. These units range in height from 63 inches for the G.E. unit to 82 inches for the A.O. Smith unit. Check the manufacturer’s specs before placing your order.
  • The location must allow for the installation of a condensate drain. If a gravity drain (a floor drain) isn’t possible, you’ll need a condensate pump. Since a 120-volt condensate pump that is plugged into a GFCI receptacle will stop working every time the GFCI has a nuisance trip, you probably want to order a 240-volt condensate pump and have it hard-wired.
  • The proposed location must be roomy enough to allow for proper airflow around the unit and for proper maintenance of the filter, the condensate drain, and other parts.
  • The temperature of the room in which the unit is installed will drop when it is operating, by anywhere from 2 F° to 6 F° — and perhaps even more during heavy draws of hot water. The location should therefore be one where such temperature drops don’t lead to comfort problems.
  • The location must be far enough away from occupied areas (especially bedrooms) to prevent noise complaints. “The sound level is about 60 decibels,” said Aldrich. “That’s like a window air conditioner — louder than a refrigerator.”

According to most researchers, garage installations are usually the best. Garages are big, and it’s unlikely that there will be any complaints due to the unit’s cooling effect or noise. Of course, if you live in a climate that is cold enough to freeze pipes in your garage, you’ll have to find somewhere else to put it.

How much space heat do they steal?

Clearly, a heat-pump water heater scavenges heat from ambient air, thereby cooling the space where it is located. However, this is not always a problem.

  • It’s not a problem in a garage.
  • In a hot climate, even if the heat-pump water heater is located inside a home’s conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. , the unit’s cooling effect will be welcome for most of the year.
  • In a cold climate, a heat-pump water heater installed inside a home’s conditioned space will rob space heat, forcing the home’s furnace or boiler to work a little harder.

In the worst-case scenario, all of the heat scavenged by the water heater during the winter is robbed from a home’s conditioned space. However, if the unit is installed in a basement, it’s unlikely that the space heating system will need to supply all of the heat scavenged by the heat pump. After all, most basements aren’t heated directly; all they receive is indirect heat.

Assuming that the basement in not used as living space, some but not all of the heat scavenged by the water heater will come from the furnace, and the basement will stay a few degrees cooler than it would have been otherwise. For many homeowners, cooler basement temperatures aren’t a problem. The fact that there is a slightly higher delta-TDifference in temperature across a divider; often used to refer to the difference between indoor and outdoor temperatures. between the first floor and the basement will have only a very small effect on the home’s heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load..

Quantifying these interactions is extremely tricky. “It’s a crazy thing to try to model,” said Robb Aldrich. “So what we have done is to try to bracket it. If the heat-pump water heater robs no heat from the space” — for example, if the unit is in a garage — “then all the measured electrical savings are really savings. On the other hand, the worst-case scenario would be if the heat-pump water heater operated in resistance-only mode for six months of the year. That’s unlikely; it’s the worst-case scenario. What this means is that from the standpoint of energy consumption, a heat-pump water heater is almost always going to be better than just electric resistance, and often quite a bit better. Yes, the heat is coming from the space during the winter, but not every BTUBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. that you take from the basement needs to be replaced by the heating system; that percentage will vary widely.”

Can the exhaust air be ducted outdoors?

At least one heat-pump water heater manufacturer (AirGenerate of Houston, Texas) allows the exhaust air from the heat pump to be ducted to the outdoors. The idea is that if your heat-pump water heater is making your utility room too cold, you might want to send the cold exhaust air somewhere else.

There’s only one problem with this approach. According to David Kresta, a project manager at the Northwest Energy Efficiency Alliance in Portland, Oregon, the temperature of the exhaust air coming off of a heat-pump water heater is in the range of 45°F to 60°F. If you send all of that exhaust air out of the house, an equal volume of makeup air will enter the house from the outdoors. If the outdoor temperature is lower than the temperature of your exhaust air, you’ve made your house even colder than it would have been if you had exhausted the heat-pump inside your house.

Not only that, but the exhaust fan will have to work a little harder (and use a little more electricity) to send the exhaust air through ductwork than it would to just blow the air in your utility room.

How much will I save?

Robb Aldrich calculates that a family in New England could save between $40 and $270 per year by switching from an electric-resistance water heater to a heat-pump water heater. That calculation is based on a family that uses 35 gallons of hot water per day, with an electricity cost of 17 cents/kWh. (If you pay only 8.5 cents/kWh, your savings will only be half as much, of course.)

The low end of the savings scale ($40 per year) is for a heat-pump water heater installed in a bad location (a small, cold room). The high end of the savings scale ($270) is for a unit installed in a good location (a large, warm room).

According to Aldrich, the incremental cost to install a heat pump water heater (compared to an electric resistance water heater) varies from $1,400 to $2,700, depending upon which model was installed.

One of the reports that was issued by the Steven Winters researchers — “Measure Guideline: Heat Pump Water Heaters in New and Existing Homes” — includes a table with somewhat more optimistic conclusions that those summarized by Aldrich during his presentation. (Presumably, the optimistic assumption is based on avoiding bad installations in small, cold rooms.) According to the optimistic assumptions, a family using 35 gallons of hot water per day can expect annual energy savings of 1,750 kWh. If electricity costs 12.6 cents/kWh, the annual saving is $221, and the payback period is 6.6 years (based on a relatively low incremental cost of $1,458 to install the heat-pump water heater).

Families that use more than 35 gallons of hot water per day can expect a shorter payback period.

Choosing a heat-pump water heater

When it comes to integrated heat-pump water heaters — that is, units that come with a tank — five models dominate the market:

  • AirGenerate makes the ATI50 (with a 50-gallon tank) and the ATI66 (with a 66-gallon tank). The larger unit costs about $1,900 to $2,000; it has an EF of 2.40 and a first-hour rating of 75 gallons.
  • A.O. Smith makes the Voltex in two sizes (60 gallon and 80 gallon). The larger unit costs about $1,850 to $2,100; its EF is 2.33 and its first-hour rating is 84 gallons.
  • General Electric makes the GeoSpring. It has a 50-gallon tank and costs about $1,200 to $1,500. Its EF is 2.35 and its first-hour rating is 63 gallons.
  • Rheem makes the HP-40 (with a 40-gallon tank) and HP-50 (with a 50-gallon tank). The larger unit costs about $1,300; it has an EF 2.0 of and a first-hour rating of 67 gallons.
  • Stiebel Eltron makes the Accelera 300. It has an 80-gallon tank and costs about $2,400. Its EF is 2.51 and its first-hour rating is 78 gallons.

All of the researchers I talked to emphasized the benefits of a large tank size, so don’t buy the G.E. unit, the Rheem unit, or the smaller AirGenerate unit. “Bigger and hotter tanks are better,” said Aldrich. “It’s counterintuitive.”

According to “Measure Guideline: Heat Pump Water Heaters in New and Existing Homes” by C. Shapiro, S. Puttagunta, and D. Owens, “The units with smaller tanks demonstrated difficulty in maintaining hot water delivery in high demand situations, even if their electric resistance elements are used. The units with larger tanks provide a buffer in times of high demand and therefore are expected to use their heat pump for recovery, rather than reverting to electric resistance heating to maintain outlet temperature. The result is more efficient operation and better performance in terms of availability of hot water. In households with more than two occupants, a HPWH with a larger tank will likely be a better option.”

One other factor to consider: only one manufacturer (AirGenerate) makes a heat-pump water heater with a stainless-steel tank. The material used by the other four manufacturers is enameled steel. In most cases, stainless-steel tanks last longer than enameled-steel tanks.

How long will they last?

We don’t yet know how long the current generation of heat-pump water heaters will last. Nor do we know which parts will fail first — the controls, the compressor, or the tank.

When I asked Aldrich about the longevity of these units, he said, “That’s a big question. I am cautiously optimistic. Ten or 12 years ago, we did a study of the early models available, and we noticed failures during the first few years after the units were installed. We are not seeing anything like that now with the newer units. The controls are more robust. If you think of a refrigerator, how long does a fridge last?”

So I asked a follow-up question: “Well, would you put one in your own house?”

He answered, “If I didn’t have natural gas — yes, I would.”

Last week’s blog: “Are Tankless Water Heaters a Waste of Money?”

Tags: , ,

Image Credits:

  1. A.O. Smith
  2. GE

Apr 13, 2012 8:00 AM ET

by Jason Szumlanski

"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

Apr 13, 2012 8:07 AM ET

Edited Apr 13, 2012 8:09 AM ET.

Response to Jason Szumlanski
by Martin Holladay

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.

Apr 13, 2012 8:17 AM ET

Edited Apr 23, 2012 4:40 PM ET.

HPHW units have many less than ideal issues imo
by aj builder, Upstate NY Zone 6a

Expensive product, that may not save in many ways in Northern NY imo..

Worthy discussion and needed though, thank you Martin and GBA

Apr 13, 2012 8:23 AM ET

Another Option
by Don Purington

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:

Apr 13, 2012 8:27 AM ET

Edited Apr 23, 2012 4:47 PM ET.

Response to AJ
by Martin Holladay

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.]

Apr 13, 2012 8:30 AM ET

Edited Apr 13, 2012 9:08 AM ET.

Response to Don Purington
by Martin Holladay

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.

Apr 13, 2012 11:54 AM ET

Edited Apr 13, 2012 11:55 AM ET.

noise reduction
by Jason Miller

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.

Apr 13, 2012 12:03 PM ET

Response to Jason Miller
by Martin Holladay

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.

Apr 13, 2012 12:18 PM ET

Attic Installation
by Cameron Moore

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

Apr 13, 2012 12:25 PM ET

One clever idea....
by Jim Hassi

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.

Apr 13, 2012 12:35 PM ET

Response to Cameron Moore
by Martin Holladay

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.

Apr 13, 2012 12:38 PM ET

Response to Jim Hassi
by Martin Holladay

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.

Apr 13, 2012 12:53 PM ET

Response to Martin Holladay
by Cameron Moore

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.

Apr 13, 2012 12:59 PM ET

Response to Cameron Moore
by Martin Holladay

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.

Apr 13, 2012 1:34 PM ET

Edited Apr 13, 2012 1:35 PM ET.

Radiant Floors
by Scott McCullough

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?

Apr 13, 2012 1:47 PM ET

Edited Apr 13, 2012 2:45 PM ET.

Response to Scott McCullough
by Martin Holladay

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.

Apr 13, 2012 2:54 PM ET

Notice to readers
by Martin Holladay

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.

Apr 13, 2012 3:47 PM ET

Edited Apr 23, 2012 4:45 PM ET.

Heat Pump Water Heaters may not have come of age
by aj builder, Upstate NY Zone 6a

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.


Apr 13, 2012 3:58 PM ET

Edited Apr 13, 2012 4:34 PM ET.

Response to AJ
by Martin Holladay

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.

Apr 13, 2012 3:59 PM ET

The unanswered space heating impact question...
by Dana Dorsett

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.

Apr 13, 2012 4:05 PM ET

Response to Dana Dorsett
by Martin Holladay

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.

Apr 13, 2012 4:06 PM ET

Ducting HPWH to refrigerater coil
by John Semmelhack


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!

Apr 13, 2012 4:11 PM ET

Response to John Klingel and John Semmelhack
by Martin Holladay

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.

Apr 13, 2012 5:24 PM ET

Edited Apr 23, 2012 4:47 PM ET.

Repetitious post edited.
by aj builder, Upstate NY Zone 6a


Apr 13, 2012 6:03 PM ET

re fridges etc
by Keith Gustafson

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.

Apr 13, 2012 6:13 PM ET

benefits of exhaust air ducting
by Dave Kresta

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.

Apr 13, 2012 6:36 PM ET

Overly pessimistic? I doubt it. Response to Martin
by Dana Dorsett

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 in the low to mid-50s even with the room heated constantly to 65F.) So the cost of heating the water is still highly dependent upon the cost & efficiency of the space heating fuel & equipment. It's a huge elephant in the room that needs careful consideration before making broad recommendations, particularly for locations in US climate zones 5 & higher with 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.

Apr 13, 2012 10:51 PM ET

Not me
by John Klingel

"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.

Apr 14, 2012 7:48 AM ET

Edited Apr 23, 2012 4:51 PM ET.

an unnecessary gadget?
by aj builder, Upstate NY Zone 6a

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?"

Apr 14, 2012 11:31 AM ET

Get real people
by David Taormina

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?

Apr 14, 2012 9:04 PM ET

Edited Apr 14, 2012 9:07 PM ET.

Response to several
by Curt Kinder

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.

Apr 16, 2012 11:23 AM ET

Edited Apr 16, 2012 11:25 AM ET.

Lovely Discussion
by Edgar Lopez

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.

Apr 18, 2012 4:48 PM ET

Heat Pump Water Heaters
by 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? I do not want to use a hot water circulation pump.

Apr 18, 2012 4:56 PM ET

by bo jespersen

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.

Apr 18, 2012 4:56 PM ET

Attic Installation/Cameron Moore
by Kohta Ueno

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.

Apr 18, 2012 5:09 PM ET

by Tom Gocze

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

Apr 18, 2012 5:19 PM ET

Reply to Edgar Lopez
by Kevin Dickson, MSME

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.

Apr 18, 2012 8:16 PM ET

Edited Apr 18, 2012 8:23 PM ET.

Heat Pump Hot Water Services
by Stan Smith

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!

Apr 19, 2012 12:20 AM ET

Not as new as it seems!
by Peter James

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.

Apr 19, 2012 7:17 AM ET

Response to Edward Acker
by James Morgan

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.

Apr 19, 2012 8:08 AM ET

a good match with ground source heat pump?
by janet bergman wilkinson

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.

Apr 19, 2012 10:19 AM ET

Response to Edward Acker
by 5C8rvfuWev

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.

Apr 22, 2012 1:44 PM ET

Response to Dana Dorsett
by Martin Holladay

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.

Apr 22, 2012 1:50 PM ET

Edited Apr 22, 2012 1:51 PM ET.

Response to Edward Acker
by Martin Holladay

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.

Apr 22, 2012 1:55 PM ET

Edited Apr 25, 2012 6:03 AM ET.

Response to Bo Jespersen
by Martin Holladay

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.

Apr 22, 2012 2:00 PM ET

Response to Kohta Ueno
by Martin Holladay

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).

Apr 22, 2012 2:06 PM ET

Edited Apr 25, 2012 5:09 AM ET.

Response to Janet Bergman Wilkinson
by Martin Holladay

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).]

Apr 23, 2012 9:31 AM ET

Edited Apr 23, 2012 9:32 AM ET.

Not a bad product, just bad applications
by Michael Plehn

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.

Apr 23, 2012 10:24 AM ET

Edited Apr 23, 2012 10:26 AM ET.

Other advantages of HPWHs
by Andrew Alden

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.

Apr 23, 2012 9:35 PM ET

Oil Fired Hot Water
by Steve Rust

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.

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