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Musings of an Energy Nerd

Revisiting Heat-Pump Water Heaters

A survey of appliances available to North American buyers

A.O. Smith, a well-known manufacturer of heat-pump water heaters, sells its water heaters under ten different brand names: A.O. Smith, American, GSW, John Wood, Kenmore, Lochinvar, Reliance, State, U.S. Craftmaster, and Whirlpool.

About six years ago, I wrote an article for GBA called “Heat-Pump Water Heaters Come of Age.” Since then, manufacturers’ offerings have changed significantly, so it’s time for a fresh look at available equipment.

My 2012 article mentioned five manufacturers of heat-pump water heaters: AirGenerate, General Electric, Stiebel Eltron, A. O. Smith, and Rheem. Two of these manufacturers have left the market. The first manufacturer to drop out was AirGenerate. (For more on AirGenerate’s trials and tribulations, see “AirGenerate and Electrolux Tier 2 Heat Pump Water Heater Units Removal.”)

Toward the end of 2016, General Electric announced that it would stop making its GeoSpring heat-pump water heaters. A few months later, however, a rival manufacturer, Bradford White, purchased GE’s manufacturing equipment and began producing GeoSpring lookalikes under the Aerotherm brand. (For more information on GE’s exit from the heat-pump water heater market, see “Bradford White Buys GeoSpring Rights and Equipment.”)

Bradford White sells the Aerotherm in two sizes. The 50-gallon model has a first-hour delivery rating of 65 gallons, while the 80-gallon model has a first-hour delivery rating of 87 gallons.

Stiebel Eltron, the well-known German manufacturer of heat-pump water heaters, is still going strong, as are two American manufacturers, A.O. Smith and Rheem.

Stiebel Eltron’s heat-pump water heaters are branded as Accelera heaters. They are available in two sizes. The 58-gallon model has a first-hour rating of 50 gallons, while the 80-gallon model has a first-hour rating of 74 gallons.

For any consumers trying to make sense of the heat-pump manufacturing market, there’s a perplexing wrinkle to the story. The two best-known American manufacturers, A.O. Smith and Rheem, allow a very large number of appliance distributors to slap their own labels on the water heaters that they manufacture. The result is confusion.

A.O. Smith sells Voltex heat-pump water…

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33 Comments

  1. Josh Durston | | #1

    What about the Nyle Geyser, it's a split style that connects to the tank view piping or hoses.
    I was thinking of putting on near my woodstove to heat my hot water from the hottest room in the house. They might not be on the market anymore but seemed like a nice add-on to a electric tank.
    https://www.youtube.com/watch?v=RzJB7lD3jos

  2. User avater GBA Editor
    Martin Holladay | | #2

    Josh,
    As far as I know, Nyle no longer manufactures its Geyser water heater (a heat-pump water heater for residential customers). The odd quirk about the Geyser unit was that it didn't come with a tank.

    The Nyle web site lists equipment designed for large commercial users of hot water, but doesn't list any equipment designed for residential use.

  3. Will Campbell | | #3

    I recently installed a Rheem 80 gallon HP water heater. It's so quiet I have to put my hand on the exhaust duct to tell for sure if it's running.

    The app tells me that I've used about 45 KWH of energy in the last 30 days. That's $5.87 at our current $.13/KWH net rate. Family of two adults, one of which isn't very energy-conscious. :)

    It cost about $2500 all up, including a $300 electric bill to run power to the unit (replacing two gas water heaters plumbed in series).

  4. Jamie Wolf | | #4

    We've been hearing anecdotally about corrosion problems with Steibel coils (requiring replacement). This was brought to light because we had a problem with coil corrosion with a Fujitsu ducted minisplit (they replaced it) which led to research on "formicary corrosion" which it turns out, has become (according to our HVAC sub) an industry wide problem, especially in new tighter homes, and to which Lennox and American Standard have responded by switching to aluminum coils.

    I'd love to hear what you could dig up or report on all this - seems like something we'd all like to know more about.

  5. Derek Roff | | #5

    Cost comparisons look very challenging. Is there any way to compare the overall cost and the total energy consumption over time between a new, plain, resistance electric water heater and a few of these heat-pump water heaters, for some common scenarios, such as family of four; retired couple, etc?

  6. User avater GBA Editor
    Martin Holladay | | #6

    Derek,
    For a discussion of possible cost-saving scenarios, see my earlier article, "Heat-Pump Water Heaters Come of Age."

    Briefly,
    1. If you currently use natural gas to heat domestic hot water, a heat-pump water heater probably won't be a cost-effective investment.

    2. If you currently have an electric-resistance water heater, and it's time to buy a new one, your payback period for the upcharge for a heat-pump water heater might be about 6 or 7 years. Families who don't use much hot water have a longer payback period, and families that use a lot of hot water have a shorter payback period.

    For a decision tree that guides homeowners through the process of buying a new water heater, see "Domestic Hot Water: No Perfect Solution."

    1. Will Campbell | | #18

      From Martin:

      "1. If you currently use natural gas to heat domestic hot water, a heat-pump water heater probably won't be a cost-effective investment."

      No doubt it depends on many factors (efficiency of previous equipment, fixed billing costs, cost per therm, cost of electricity, varying temp of incoming water, usage, etc) but in our case, it appears to be about a 6-7 year payback to go to the HPWH we did, comparing the delta cost against another conventional heater. Our old heaters were 18 years old at the time we replaced them, and they were still working well; we just thought it was time to replace them prophylactically.

      We typically get 15-20 years out of a water heater, so we should be well ahead over time, assuming that the new HPWH is as reliable as the simpler ones we've had in the past (possibly a dangerous assumption!) But we'll still be ahead even if it only lasts a third as long as the previous ones.

  7. Andy Kosick | | #7

    Is this correct? It seems backwards.

    "Stiebel Eltron’s heat-pump water heaters are branded as Accelera heaters. They are available in two sizes. The 58-gallon model has a first-hour rating of 50 gallons, while the 80-gallon model has a first-hour rating of 74 gallons."

    1. Brian Bailey | | #12

      Andy -

      I believe the confusion stems from two things.

      First, because cold water mixes with the hot as the water heater is drawn down, you can't generally get all the hot water from the tank at the setpoint temperature.

      Second, I think the Steibel units use only a heat pump to heat the water; the other systems are "hybrids" meaning they use a heat pump but also have a regular electric resistance unit which kicks on in certain situations. The hybrid units are capable of a first-hour delivery larger than their tank sizes because the resistance heaters can activate after the hot water is drawn down by a certain amount.

  8. User avater
    Albert Rooks | | #8

    Hi Martin,

    Thanks for the update on the unitary systems. While the first cost of these systems are attractive I think it would be good service to schedule an update on the split system discussion. The Sanden SanCo2 has been in the market for a few years now and it’s done exceptionally well. Compared to the unitary systems, it’s far more efficient, far more versatile, and far less damaging with the low GWP refrigerant. Not to go off on a tangent, but I think most are aware that global refrigerant use is at a quick increase and the potential damage they can bring is capable of undoing much of what we’ve done with envelope improvements.

    At this point, I’ve participated in various field study trials, our company Small Planet Supply has sold LOTS of systems across USA and Canada (along with many other dealers) and the instals have had great success. The new gen three has the ability to deliver between 130f and 175f. Add a new a 119 gallon tank, and you can image the systems being designed now can serve multifamily buildings with 119 gallons of 175f water that will mix down to serve multiple units. The internal gains are are reduced with short distribution runs and that’s just a start. I’ll attach a pic from this weekend presentation in Seattle by Ecotope showing four heat pumps ganged up on a large tank.

    The single family application are just plain simple and far better than unitary systems.

    In short, while the HPWH discussion here starts with a single family home, we have more solid options for all building types than are listed, and the first cost price tags comes with an unaccounted for global cost that we all will pay if we don’t consider refrigerant GWP into our thinking.

    It’s probably time to do a deeper dive into where the split system is today. There’s far more post installation data and new uses than I can put into the comment section here.

    Thanks for your continued work:)

  9. User avater GBA Editor
    Martin Holladay | | #9

    Response to Andy Kosick (Comment #7):
    Andy,
    I'm not sure what aspect of my reporting seems "backwards" to you. The water heater with a larger tank has a higher first hour rating -- that seems logical to me, not backwards. See the image below.

    1. Andy Kosick | | #10

      That was a poor choice of words and too vague of a question, I didn't mean to imply anything about the quality of your reporting. What seems strange, even for a heat pump, is that the first hour rating is less than the tank capacity. What would account for this?

  10. User avater GBA Editor
    Martin Holladay | | #11

    Andy,
    Q. "What seems strange, even for a heat pump, is that the first hour rating is less than the tank capacity. What would account for this?"

    A. First of all, there is always some thermal stratification in any hot water tank. The water near the top of the tank is at a higher temperature than the water in the bottom of the tank.

    As hot water is drawn out of the top of the tank, cold water flows into the tank. The incoming cold water is introduced at the bottom of the tank. If you have a 58-gallon tank of hot water, you can get about 50 gallons of hot water out of the tank during the first hour. After 50 gallons of hot water are drawn from the tank, the 51st gallon of water is a little cool (due to the fact that lots of cold water has been flowing into the tank over the last hour), and the homeowner is no longer satisfied with the shower. At that point, you need to turn off the shower and let the water heater catch up.

  11. User avater GBA Editor
    Martin Holladay | | #13

    Response to Albert Rooks (Comment #8),
    I have no doubt that the Sanden water heater performs well. We've heard from GBA readers, however, that the installed cost of this water heater is between $3,600 and $5,900. That high cost lengthens the potential payback period.

    If a family is now paying $400 per year to operate an electric-resistance water heater, they might save $250 a year by switching to a Sanden. But if the upcharge for the new equipment is $4,000, the simple payback period is 16 years.

  12. User avater
    Michael Maines | | #14

    Martin, I don't think the Sanden is worth dismissing out of hand, for those willing to invest in higher performance. While it's hard to beat the return on investment of installing a one-piece heat pump water heater, using your numbers of a $250 annual savings and an upcharge of $4,000, that's a simple return on investment of 6.25%. Assuming 3% inflation, the upgrade would pay for itself in 15 years. While not an amazingly highly ROI, it's pretty much guaranteed, and likely better than the stock market will be doing in its next cycle.

    While the first costs are expensive, certainly too rich for my wallet, I regularly talk clients into energy improvements with ROI of 5% or lower. And I'm not a very good salesperson. (I find it hard to recommend improvements once we get into the 2% to 3% territory, but it's not my money, and there are often environmental positives even at those returns.)

    The refrigerant issue is also significant. As you know, conventional refrigerants are potent global warming agents, a thousand times worse than CO2 in the atmosphere.

  13. User avater GBA Editor
    Martin Holladay | | #15

    The comment posted below was authored by a GBA reader named Jan Juran, who sent me the comment by email:

    "Hi Albert and Martin: I recently installed a Rheem Performance Platinum heat pump HW heater in my Long Island NY home zip code 11976. Uniform Energy Factor 3.55; 67 gallon first hour rating; $1299 at the local big box store for model XE50T10HD50U1; plus $500 for my plumber to install it. Energy Star's protocol estimates a yearly electricity use of 915 KwHr. PVWatts estimates that 650 watts of PV added to my grid tied PV array will produce these 915 KwHrs per annum; the local PV installer will do it for $2.45 per watt after 30% tax credit=$1600 for enough PV to run it for 30+years. Total: $1300+500+1600=$3450 installed, or less than the low end installed cost of a Sanden CO2 system. Benefits include zero electricity cost/GWG/pollution plus the PV system will still generate long after the HW heater wears out. (The value of the free AC during summer and basement dehumidification exceeds the winter heating energy penalty for the air source heat pump HW heater in my case. The local recycling center provides proper disposal and refrigerant recapture for $5).

    "Allow us to cheer enthusiastically from the sidelines as Sanden improves the price/performance of its innovative design over time. In the interim, there is a better solution in locations where PV is feasible."

    -- Jan Juran

  14. Andy Kosick | | #16

    Response to Martin (comment #11) and Brian Bailey (comment #12)

    Thanks for the explanation. What Brian said about the Steibel units not being "hybrid" seems important and perhaps more the reason for my confusion.

    This article was very timely in that I recently needed to spec a HPWH for a Habitat project and did some research on a few brands. I'll admit that I eliminated Steibel immediately because of price. All the 50 gallon models from Bradford White, Rheem, A.O. Smith had First Hour Ratings above their tank capacity and all models were also hybrid. The big question this leaves me with is do these FHRs include the resistance coils coming on and the Steibel alone reflect the capactiy of a HPWH in Heat Pump Only mode.

    Of the 114 active HPWHs in the AHRI database 7 have FHRs less than the capacity. In some cases the same model under a different brand name had a higher FHR than capacity, this just makes me think controls might have something to do with it. A brief look across the web had quite a bit of info about the FHR and UEF tests but nothing as to which setting the Hybrids were in for the test and whether or not the coils came on at any point.

    The relevance here is that if you want the these units to operate as a HP all the time for maximum efficiency, like I do, and coils to only come on once a year when the whole family visits at Christmas, the first hours ratings may be misleading for sizing the unit. I ended up with the Rheem XE50T10HD50U1 for the Habitat project and the article and comments here have given me a good feeling about that. That said, capacity was certainly part of the consideration because I know HPWHs have a slow recovery but I'm wondering if when set to Heat Pump Only is the Rheem going to have the 67 gallons it's rated at available or more like 45 gallons in the first hour? While I have no significant concerns about this project, it would frustrating to end up in Hybrid Mode with the coils coming on once a day at a significant energy penalty.

  15. User avater GBA Editor
    Martin Holladay | | #17

    Andy,
    The first hour rating test procedure is set forth in a federal law, 10 CFR Appendix E to Subpart B of Part 430, "Uniform Test Method for Measuring the Energy Consumption of Water Heaters."

    The relevant part of the federal statute reads:

    "For heat pump water heaters, if a default mode is not defined in the product literature, each test shall be conducted under an operational mode in which both the heat pump and any electric resistance backup heating element(s) are activated by the unit's control scheme, and which can achieve the internal storage tank temperature specified in this test procedure; if multiple operational modes meet these criteria, the water heater shall be tested under the most energy-intensive mode. If no default mode is specified and the unit does not offer an operational mode that utilizes both the heat pump and the electric resistance backup heating element(s), the first-hour rating test and the simulated-use test shall be tested in heat-pump-only mode."

    In other words, how the test is conducted depends on the manufacturer's definition of the default mode.

    1. Trevor Lambert | | #25

      So the decision sequence goes like this:
      Does the unit have a default hybrid mode? If yes, use this mode.
      Does the unit have any hybrid mode at all? If yes, use the one with the highest energy consumption.
      Else, use the heat pump mode.

      So the only cases where the electric coils would not be part of the test are if they don't exist, or the unit has only either/or operation, no hybrid mode. I'd be surprised if such a model existed.

  16. Sam Clarkson | | #19

    I'm just starting my homework to set up Spa pool heating via heat-pump. This is for a hotel, and I'm looking to relocate a number of refrigeration units from outdoors to an indoor 'machine room', then to recover the resultant 'waste' heat to heat the spa. (with the added 'by-catch' of dehumidifying a rather damp basement area).
    Ant articles, or advice, gladly devoured.
    I'm in New Zealand, in case that matters, where the water goes down the plug-hole the CORRECT way!

  17. User avater GBA Editor
    Martin Holladay | | #20

    Sam,
    As I'm sure you know, a compressor connected to a water heater will lower the temperature of the room where it is located -- not raise it.

    If you have a compressor connected to a commercial refrigerator or an air conditioner, it will raise the temperature of the room in which it is located. But be careful -- you would need an extremely large room for this strategy to work, because the room can quickly overheat, affecting unit efficiency. That's why commercial refrigeration and air conditioning compressors are usually located outdoors.

    For more information on this issue, see "Does a Heat Pump Condenser Need to Go Outdoors?"

    1. Sam Clarkson | | #22

      It is a big room, or to be precise, series of rooms. I envisage an entire circulation of air that will scavenge the waste heat from the refrigeration units, the sauna, spa, drying room, gym, ski hire and turn it into spa hot water. the resultant cold, dry air will then circulate through damp basement ducts and eventually back to the gym, sauna etc. Size of this complex of rooms/ at least 17m x 20m x 2.7m high. That's a lot of volume... That's a TON of waste heat. I weep at the current wastage.

      1. User avater
        Peter Engle | | #26

        Sam,

        I share your thoughts, and have toyed with the same approach to scavenging waste heat. I've done this already several times on a small scale, but so far nothing like the system you describe. I did some conceptual design for a winery, since they require both heating and cooling of the tanks and spaces, often at the same time. Unfortunately, that facility was never built. My biggest concern with this approach is load matching, both in time and over time.

        By that, I mean that you need to be careful that the loads exist at the same time. If, for example, the spa requires heat at a certain time and the other spaces require chilling at different times, you might see significant temperature swings. If the loads are not balanced in total over time, you could see the average temperature of the spaces drifting quite a bit.

        In either case, your HVAC system will have to deal with these unbalanced loads and in some cases, that could significantly offset the savings of using scavenged heat. You can also have seasonal effects that make all of this more complicated.

        I believe that there are some dramatic energy savings possible with this sort of scavenged (or shared) heat approach in commercial and industrial spaces, but you really need to do some careful math to verify proper performance before jumping into this.

        Let us know how it goes!

        1. Sam Clarkson | | #30

          So complicated that I'm tempted to say it's almost impossible to model?
          It's not a big spa pool and, while it will take a bunch of heat to heat it up form cold, once up to temp it's just a matter of maintaining that heat. That will include the heat that 'evaporates' off said water into the spa room being scavenged back through the heat pump. Plus all the (currently) waste heat from gym, sauna etc.
          Anyone have any suggestions as to how to model it?

  18. Jean Terwilliger | | #21

    Another vote for the Rheem- 50 gallon in this case. Have been running it in my new net-zero house for about four months. Chose it for it's easy ducting capability. We have it tucked under the stairs in our small utility room, with the cool exhaust ducted into our pantry. It's quieter than any other appliance in my house- don't even notice when it's on. It's not metered separately, so don't know exactly how much energy it's using on all heat pump mode. It nicely covered showers for a houseful of guests in "hybrid" mode.

  19. Rob Hunter | | #23

    With regard to the 1000 cf room size requirement, could the HPWH be located in a small but dry enclosed outdoor space with intake and exhaust ducts?

  20. User avater GBA Editor
    Martin Holladay | | #24

    Rob,
    Q. "Could the HPWH be located in a small but dry enclosed outdoor space with intake and exhaust ducts?"

    A. There are two issues here: Issue #1 is whether you can install a heat-pump water heater outdoors (where the plumbing is at risk of freezing). Issue #2 is the minimum volume of a mechanical room that houses a ducted HPWH.

    Issue #1: Can you install a HPWH outdoors? No, not unless you live in a frost-free location like low-altitude areas of Hawaii. Frozen pipes aren't fun.

    In Florida, water heaters can be installed in an attached garage. If you need more advice on the likelihood that pipes will freeze in your climate, talk to a local plumber.

    Issue #2: Adding ducts to a heat-pump water heater changes the performance of the water heater. Note that not all brands of HPWHs allow for ducting, so if you want to attach ducts to your HPWH, you will need to (a) choose a HPWH (like one from Rheem) that allows ducting, and (b) contact the manufacturer to determine maximum duct lengths and the minimum required volume of the room where the appliance will be located.

    Here is a link to information on ducting kits for A.O. Smith heat-pump water heaters: "Ducting Kit Installation Instruction for Hybrid Electric Heat Pump Water Heaters."

    Adding ducts to a HPWH increases energy use (since the HPWH fans have to overcome the static pressure of the ducts) and changes the temperature of the air from which the HPWH extracts heat. (In some climates, the outdoor air in winter is colder than indoor air.) For more information on the net affects of these factors, see these research papers:

    "Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort"

    "Heat Pump Water Heater Ducting Strategies with Encapsulated Attics in Climate Zones 2 and 4"

  21. user-6765831 | | #27

    We are planning to install a fully ducted Rheem HPWH under our stairs. Has anyone here ever specified or built a way to easily move the exhaust ducting from the outdoors to the indoor space during the cooling season? Seems like a "wall-cap" would be needed, at a minimum, to cover the area of the vent from the indoors. Probably need to reattach the duct to some kind of vent that would then exhaust the air into the indoor space. Does this seem a wacky thing to try to do?
    Asaf

  22. Rob Hunter | | #28

    Martin, thanks for the links. I read the articles and my top line takeaway is that ducts are basically fine as long as both supply and return ducts are used; efficiency drops significantly if only one is used. I could make the space I'm thinking about part of the conditioned envelope, but it wouldn't be ideal.

    How about putting the heat pump in (conditioned) roof truss space? Other than weight, and the liability of a water line in the ceiling, is this a common practice?

  23. User avater GBA Editor
    Martin Holladay | | #29

    Rob,
    Q. "How about putting the heat pump in (conditioned) roof truss space? Other than weight, and the liability of a water line in the ceiling, is this a common practice?"

    A. Is it common? No. Heat-pump water heaters are usually installed in a basement or a mechanical room, or (in warm climates) in an attached garage.

    Is it possible? Yes, if the unit is ducted, and if you are willing to put up with the listed liabilities. Remember that you need access to the space for maintenance and eventual replacement.

    1. Rob Hunter | | #31

      Unfortunately, the garage is detached and the mechanical room just bit the dust courtesy of northern California's unbelievably high concrete costs (north of $1K/yard!). The conditioned crawl space has just 24" of clear space below the joists, so the only way to use it for the water heater would be to excavate a bunker for it - which may be the only good option, because I'm not excited about putting a 300+ pound cylinder of hot water 10 feet in the air with no good way to control the inevitable flooding when the water line intake corrodes out in 10 years...

  24. Rob Hunter | | #32

    wonder why no one makes a low boy heat pump water heater? I suspect a lot of others are paddling the same leaky boat I'm in...

  25. User avater GBA Editor
    Martin Holladay | | #33

    Rob,
    If your designer didn't plan ahead and include a mechanical room that is big enough for all of your planned mechanical equipment, you're between a rock and a hard place. You may end up installing an electric-resistance water heater.

    Perhaps you can balance the higher electricity usage with a PV system -- assuming, of course, that your local utility offers a decent net-metering contract.

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