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Q&A Spotlight

Heat-Pump Water Heaters in a Cold Climate

Factors to consider when transitioning to all-electric heat-pump technology

Heat-pump water heaters borrow heat from the area where they are installed. But when installed in a basement, heat losses shouldn't be a significant problem. These units are being tested at the Oak Ridge National Laboratory, which supplied this photo.

Moving to a fully electrified home eventually means replacing a water heater fired by gas or oil with one powered by electricity, and by far the most efficient option is a heat-pump water heater.

But because these appliances borrow heat from indoor air to heat water, are they a good choice for houses built in cold climates? That’s what’s on the mind of Michael Sterner, who shares his concerns in this recent Q&A post.

“Currently building a Pretty Good House in Northern Wisconsin,” Sterner writes. “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 minisplit with air handler. Naturally, I am thinking about a heat-pump water heater as well. ”

He’s considering a 50-gal. Voltex hybrid model made by A.O. Smith ($1710 through, which promises “excellent performance in cool climates.” Sterner has seen good reviews of models like this in warm climates.

“But what about in a cold climate?” he asks. “Any measures that need to be taken, or special things that I should know about?”

That’s the topic for this Q&A Spotlight.

Noise may be an issue

Kyle R has the same unit that Sterner is considering, and he reports that placing it in the basement of his Michigan home has not created a noticeable temperature problem. Noise, however, is another story.

“It works, but it’s quite loud,” Kyle says. “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.”

Kyle suggests doing some research on units that would be quieter, and he would consider a water heater with more capacity so…

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  1. tekjunkie28 | | #1

    I have been wanting one of these but they are just too expensive and the price has gone up several hundred in just 1 year.

    A side note... the Rheem gen 5 seems to have a issue with some of them that the compressor is too loud. This has been fixed by Rheem and the remedy was a completely new unit.

  2. jonny_h | | #2

    I'd love to get one of the Sanden units -- it just seems to make sense from an engineering standpoint. In a zone 5 climate, it's not taking heat from indoors during half the year (which decreases its theoretical COP, since the input heat needs to come from some other source with its own COP). In fact, with a bit of hydronics added, it can be used as an auxiliary heat source. Also, the CO2 refrigerant is plus, compared to all the other typical systems. However, there are several downsides that have stopped me so far:

    - Presumably since (in the US) there's only one supplier and it's a niche imported product, the cost is substantial. This is the biggest barrier, at 3-2x the cost of the more traditional systems.
    - The water lines between the outdoor unit and the storage tank need to be well insulated and heat-traced, and a prolonged power outage or system failure during cold weather risks freezing & destroying the outdoor unit. The "solution" here is a complicated drain-back valve system. This drawback seems to be the paradoxical thing about how these units are designed -- CO2 refrigerant excels at high-temperature-lift applications, and sourcing heat from outdoors makes the most sense in cold climates. However, placing water lines outdoors seems to limit the application to warmer climates, where the temperature difference isn't as high, and heat stolen from indoors probably helps reduce cooling load more often than it increases heating load.

    Ideally what I'd like to see would be a CO2-refrigerant split system -- only refrigerant lines running outdoors, not water, but keep all the other benefits of having the source-side coil outdoors and using CO2 refrigerant. Manufacturers, get busy!

    1. charlie_sullivan | | #4

      The challenge in making a split CO2 system is that the refrigerant lines run at much higher pressure than conventional refrigerants. So you need special lines and special assembly methods. That may be coming but it isn't easy.

      1. brendan_kavanagh | | #7

        The Sanden, now called SANCO2, has all the CO2 refrigerant components in the outdoor unit and only exchanges water with the tank inside. Therefore all the refrigerant components are factory made but you'll need to be careful about protecting the water lines in cold climates.

  3. luke_p | | #3

    I have been thinking that using a tempering tank before a regular resistance hot water tank would be useful for gaining at least some of the energetic advantage of my heat pump. Here in Montreal, the city water supply can come it pretty cold, like 4 C in the winter, so bumping that up to 19 or 20 in the tempering tank is still a 15 degree increase using heat from the heat pump before it goes into the regular hot water tank. Even in summer the city water is coming in colder than room temperature so there would still be advantages albeit much less.

  4. charlie_sullivan | | #5

    To clarify my comment quoted in the article: I am not recommending switching off the heat pump in the winter for a typical installation. Rather, I am pointing out that in the unlikely event you are unhappy with its behavior in the winter, you have the option to revert to regular electric heat. And pointing out that even if you only use the heat pump half the year, you'll save substantial energy compared to an electric resistance water heater.

    One more clarification: I don't think anyone should worry about their HPWH drying the air excessively in the winter. Once you reach the point where humidity is reasonable, it will stop removing moisture and only remove heat.

  5. qofmiwok | | #6

    Great article. I am building now and need to decide soon. But with only 2 people and low water use, my estimated power use is low even for electric resistance. Plus I'm in a heating climate almost year round. So my inclination is to pass for now. Especially since my heat pumps are all upstairs and I'm heating the crawl with electric resistance. That changes the equation a bit.

    It doesn't help that I've seen a ton of issues on HVAC forums about the Gen 5. Not just noise but leaks and other failures. I wonder if they have all been addressed.

  6. JRK_Labs_com | | #8

    I'm contemplating using this product in our future basement with an indirect hot water tank,

    Basically building my own heat pump hot water heater using more robust components (and possibly multiple heat sources).

    1. charlie_sullivan | | #9

      Nyle has often had "coming soon" products like that on their web site. I think it's great if it's available, but I'm not clear on whether or when it really is available.

      1. JRK_Labs_com | | #10

        Hi Charlie, the word that I've received from Nyle is that it should be available late Q1 of next year. Our house will still be under construction then so I'm hoping that the timing aligns.

        1. charlie_sullivan | | #11

          If that happens, that would be great!

          1. Phimnoi | | #12

            I received an EMAIL from Nyle 2 days ago telling me that the e8 will be available in April, 2022.


          2. charlie_sullivan | | #13

            Thanks--I might plan to install one in the spring then!

    2. rajibroy | | #15

      Hello JRK LABS
      Am also building a single family home with an accessory dwelling unit in Vermont (zone 6a). Sanden system seems super costly compared to indoor, compact systems (Rheem or AO Smith). What's your take on Nyle vs SanC02 in regards to performance, reliability and budget.

      Appreciate your kind response.

      Rajib Roy

  7. nickdefabrizio | | #14

    I have the AO Smith 50 gal I bought at Lowes (it was a return I got for $600!). I then got a $750 NJ energy rebate. It works fine. In summer it provided nice dehumidification when running. N0w that we are in Winter (I am on the border of zone 4/5) I see it probably cools my basement 1-2 degrees or so. The noise isn't so bad. I barely notice the electric use so it seems very efficient.

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