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Community and Q&A

Heat Pump Water Heater in Cold Climate

Michael Sterner | Posted in Mechanicals on

Currently building a Pretty Good House in Northern Wisconsin. The house is nearly finished on the outside and we’re having our plumbing roughed in. 

I am using a heat pump dryer, induction stove and a heat pump mini-split with air handler. Naturally, I am thinking about a heat pump water heater as well. 

Does anyone have experience with these in cold climates? I see really good reviews of units like this in warm places like Florida: https://www.supplyhouse.com/AO-Smith-HPTU-50N-50-Gallon-Voltex-Residential-Hybrid-Electric-Heat-Pump-Water-Heater?gclid=Cj0KCQjwwY-LBhD6ARIsACvT72OZl7sJoJlpuhthir1eVnznbqsgEs_PXdwYznCWWizjYL8-m6TJyEgaAsFWEALw_wcB

… but what about in a cold climate? Any measures that need to be taken or special things that I should know about? 

I am positive that the plumber will have no idea what this is but it looks pretty straightforward to install. 

Thanks!

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Replies

  1. Kyle R | | #1

    I have the unit that you linked (50 gallon AO Smith) and the heat pump failed after a year. They are replacing it, but I still need to pull out the old one, take it to Lowes, and reinstall the new one.

    It works, but Is quite loud. My well insulated unheated basement never gets below 60 F in Michigan and the addition of the water heater didn’t change that, it does however provide significant and free dehumidification. I would do some research on the quieter units. I would also look at a bigger unit (80 gallon) at that size it should be able to run on heat pump only for most houses.

    Other than that make sure you have enough volume per the manufacturer in the room and take efforts to isolate the sound.

    1. Michael Sterner | | #2

      Hey Kyle, thanks so much!

      How loud are we talking? If it is in a basement below a kitchen, do I need to insulate the floor or is it fine if it is in a separate room?

      Is the main advantage of these over pure electrical units just the 2-3x efficiency? Is there anything else?

      1. Kyle R | | #3

        No need to insulate the floor, more like consider if you are going to finish the basement.

        Advantage is 2-3 times more efficient AND because it cools the ambient air in you basement to heat the water, it dehumidifies your basement which for me meant I could get rid of my basement dehumidifier.

  2. Kieran973 | | #4

    Do it. I'm in climate zone 5, not quite cold, southern CT. I've had a Rheem 65 gallon HPWH for almost a year and with 2-3 adult showers, one kid bath, and over-the-top handwashing every day, we're averaging 4 kwh a day. My understanding is that a with a standard electric resistance water heater we might be using 4 times that amount. The Gen 5 Rheem units have a loud compressor (the Gen 4 units apparently did not have this issue), but ours is in an unfinished basement with no floor insulation - for the first month or so, the noise mildly annoyed me when sitting in total silence on the first floor, but I don't really notice it anymore. Some other brands/units are probably quieter. But one nice thing about the Rheem is the wifi - you can change the settings from heat pump only to hybrid to vacation, etc. from your phone, which is nice if you want to save electricity while you're traveling but then have hot water right when you get back. One thing to be aware of in a cold climate: the cold dry air that the unit exhausts bothers some people if the water heater is next to a finished living space. I have some friends with an 80 gallon AO Smith unit in northern New England and their home office is in their basement, in the room right next to the water heater. They find that their workspace is noticeably chillier now than with their old electric resistance water heater. But you can just vent that cold air out of the house entirely - some heat pump water heaters (I think AO Smith?) have an optional accessory that's basically like a flex duct dryer exhaust that you can attach to the vent and vent the cold air straight outside.

    1. DCContrarian | | #5

      Venting the air outside seems to cancel the benefit of the heat pump water heater though. That air is replaced with outdoor air, and the outdoor air needs to be heated and conditioned. If it's 0F outside and the exhaust is 40F you're more than doubling the energy consumption. You're also losing humidity which can be a problem in the winter.

    2. Tim Janson | | #6

      So you vent the cold air, to then have to supply cold make up air, which gets heated by your minisplit.... my head hurts...

    3. Jonathan Blaney | | #11

      How did you deturmine your electric usage?

  3. Kieran973 | | #7

    Good points. I don't have one of these, so I hadn't thought about that - I've just heard other people on GBA talking about using and liking them in the winter. But if they just increase energy consumption, then yeah, probably not a good idea....

    1. Charlie Sullivan | | #8

      If there's a period of 2-6 months when the chill is not desired, you can switch off the heat pump and run it as a regular electric tank. And turn the heat pump back on for the rest of the year.

  4. Paul Wiedefeld | | #9

    If your layout allows for it, take a look at a drain water heat recovery unit. In a cold climate, you’ll get the energy savings of a heat pump for less money, less complexity/noise and more durability.

  5. Michael Sterner | | #10

    So, where I am at is that my house mechanicals are very much designed for the exact heat loads. We were around 27k btu/hr at peak and have a 2.5 ton heat pump with a resistance element back up in the air handler. With that, I would expect that I can't place much extra "load" in the basement during peak temps.

    So, how would I go about figuring out if the cooling effect of the heat pump water heater in our basement would cause excessive load and make it difficult to keep a comfortable basement in the winter? Or, should I just not worry about it and if push comes to shove I can turn it to electric resistance?

    I like the summertime benefits of keeping the basement cool... The basement, of course, will already stay cool from being a basement...

    I am probably more concerned about the noise than anything. It is in the basement underneath the kitchen. I definitely wouldn't want to hear it from the main floor but it wouldn't be the end of the work to hear it from the adjacent basement rooms.

    I love the idea of a drain water heat recovery unit... Unfortunately, the main shower is all the way to the west side of the house away from the mechanical room in the basement. The drain enters the septic drain and immediately leaves the building so there is limited ability to tap into that main shower as a heat source.

  6. RILEYG | | #12

    We are in climate zone 6. Have a 80 gallon AO Voltex for 4 plus years in a 1977 average insulted house. The heater is installed in the utility room in the basement which is pretty much under the master bedroom. Noise is minimal, lots of hot water, no breakdowns yet(knock on wood). We use mostly wood for heat in the winter with an electric furnace for backup. Installed some mini splits, but I cant comment on any adverse effects right now because the splits are only a few months old. The heater is great and the utility room is usually around 20 C in the winter and 17 C in the summer.

  7. Johngfc | | #13

    From first principles I don't see how a HPWH would fail to be advantageous. In summer it's a clear win. In winter, at worst, it increases your ASHP load (an energy wash but a maintenance cost). However, a basement HPWH is "drawing" heat from the basement, which presumably is interacting with (mostly) ground that's at a temperature well above air (i.e., the slab is likely never below 40 or 50 deg). Thus a HP in the basement is using air, and exchanging heat with surfaces, at a higher temperature than outside and it should therefore be more efficient. If this logic is correct, then there are likely a couple months were energy for the HPWH is a wash, but even in a cold zone (e.g. cz 6), for most months the HPWH should be (perhaps substantial) more efficient. I'm facing a similar decision so if this isn't correct please correct me!

  8. Paul Kuenn | | #14

    Hey Michael!

    Do it! The few heat pumps that break down are far and few between. We've had our HPWH for over 7 years now (company is long gone) and all works good. They do make a bit of noise but as our floors are insulated, we can't hear it. The cooling during our Sconee winters is minor. Before I did all the house insulation, the basement fell to 52 in the winter. Now it may get down to 57 (remember I didn't insulate the very bottom of foundation walls or basement slab) and only if the heat pump has been running because of 30 days worth of clouds. Solar thermal takes care of all our needs from Feb=Oct so it may last forever.

  9. Peter Sperry | | #15

    We have a Stiebel Elton 300 liter and are off grid solar so electricity consumption was critical for us. It uses around 1100 watts at 3 amps when running in what they call hybrid mode.

    https://www.stiebel-eltron-usa.com/products/accelera-heat-pump-water-heaters

    When running the only noise is the fan which isn’t loud at all. It will definitely cool the room it’s in but not the whole basement. After having it I would never go back to conventional electric or gas.

    1. Michael Sterner | | #18

      Hey Peter,
      I was closing in on this Steibel Eltron Accellera 300 unit but then I got the price. It looks like they're asking for $3,990 for this unit these days. I wonder if the price has climbed dramatically lately like everything else. Being a good $200k over budget on this house, I may have to pinch pennies and go for something else. These look really great.

  10. David Karon | | #16

    See my IG page #karoncustom

    I am retrofitting my house in Montana to the passive house building standard.

    I just installed and plumbed the heat pump, buffer tank and 20 gallon Steibel Eltron tankless water heater.

    No, I am not a plumber but I was able to get it done with confidence.

    Please reach out with questions, comments.
    You can connect with me over Instagram and we.ll go from there!

  11. Roger Berry | | #17

    Michael,

    Like you I have wondered about the impact of a HPWH on overall energy costs for a PGH. I am attaching two reports that looked into actual performance and side effects. The California based one will be less instructive for your CZ. The COP of the compressors used is of little real value in figuring out what you need to know. How efficiently you move heat means little if the cost of the heat being moved is high. In Florida the heat being moved is free almost all year. In northern Wisconsin less so since the effective bottom air temp limit for HPWH is typically about 40F. That rules out most in garage options.

    I tried to calculate the cost of using a mini-split to heat a house that then has a HPWH syphoning off some heat for hot water. It gets very complicated very quickly. Suffice to say that the longer a heating season the bigger the ding in overall efficiency against a straight up resistance heater. I concluded that in a tight home with a long heating season the advantage was less than one hopes.

    The NREL report does cover this, but it is a long slog through the report. Do pay attention to the way COP of the compressor drops as tank temps rise and the discussion of energy mangement for demand cycles. Add in noise factors and initial costs to any decisions along with spouse adjustments. I ended up getting an 80 gallon Marathon and just live with the Kwh hungry hungry hippo.

    The house is dead quiet though and a peaceable kingdom prevails.

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