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Community and Q&A

Swimming pool heat pump for domestic hot water

BrandonA | Posted in General Questions on

I am looking for an efficient way to heat water in my new ICF home.  I want to stay away from gas appliances and rely on my PV panels.  I have looked into systems such as Chiltrix, Sanden, and Daiken Altherma but they are all over $4,000.

I am also trying to avoid Hybrid heat pump water heaters as I live in  Northern Utah (zone 6B) and have read that they aren’t the quietest.

Can anyone talk me out of using a heat pump water heater such as this: ( paired with a marathon 105 gal. water heater?  I realize that it is designed for pool use but I could pair it with glycol and a heat exchanger to keep the lines from freezing. Any cautions or concerns?

Thanks,  -Brandon

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  1. charlie_sullivan | | #1

    My biggest concern is that it is probably designed for mild outdoor air temperatures and you mostly need it for quite cold outdoor air temperatures. If you can find some data on that it might be worth considering but until proven otherwise I'd basically assume it won't work.

    How are you heating the house?

  2. Aedi | | #2

    Hi Brandon,

    It would not work. It's max temp of 104F is not capable of heating water hot enough for DHW use (>130F to kill Legionnaires bacteria, and even from a comfort perspective wouldn't want less than 110F), and I doubt it has enough capacity to respond to residential water use patterns.

    If you are not using a hydronic heating system, your best bet is just to use a simple, cheap electric tank water heater. Any other options will not have reasonable payback periods; you are better off investing in water-saving measures and insulated pipes. You can set it up to run preferentially during the day (when you have more electricity) to make it more convenient.

    Edit: A recent Q&A Spotlight highlighted some common hot-water saving methods:

    Edit 2: Rereading your question, it seems like you might be suggesting using the pool water heater to preheat water going into your tank. Given the cost, meager energy savings, and potential cold-weather performance issues, it is probably a bad idea, especially for a grid-tied home with normal water usage. But it is at least possible.

  3. Expert Member
    AKOS TOTH | | #3


    You would need something that is rated at for cold weather operation (search for R410/revisible/low temp). Even with those the output temperature would be too low for DWH, but might be enough for a heating provided you have a low temp heating system in a moderate climate. Zone 6 would be pushing it.

    Take a look at:

    Hard to heat with 27C (80F) water but not impossible if you are looking for a challenge.

  4. BrandonA | | #4

    Thanks everyone, Charlie-I will be installing several mini splits for zoning purposes with radiant heating in the basement as a backup heat source. The radiant tubing is already installed as it was only $500 and I was already planning on putting 3" of foam below the slab so it was a minor cost for backup radiant. (plus another $500 for manifold/pump/heat exchanger). I don't want to rely on standard resistance marathon water heater for backup radiant as I'm afraid this might skyrocket the electric bill. would I be better off just installing an extra mini split or two in the basement? they at least have more efficiency I suppose.

    Aedi - thanks for the water saving mention, I will definitely be implementing many of these strategies. You have it exactly right, I just wanted to preheat the incoming water and top it off with the marathon.

    Akos - Do yo mean something like this?
    Would this work with a mini split?

    Thanks again!

  5. Expert Member
    AKOS TOTH | | #5

    These links from Brandon seem kind-of spammy, has the feel of pushing links for affiliate commissions.

  6. Aedi | | #6


    To my knowledge, pool heaters work by recirculating water, so they are made and rated for relatively small deltas (i.e, heating 75F water to 85F). This means they would only be able to preheat your water a small part of the way to your target temperature -- maybe 25%. Divide 25% by your expected COP for a given month and subtract from 25%, and that gives you your energy savings for that month to heat hot water. On months where you would need backup heat, that COP is likely to be less than 2.

    If these pool heat pumps actually can heat 55F water to 90F, then it might be worth it (I'd guess maybe 25% savings on the year). Otherwise, I wouldn't bother, especially considering that using them in such a fashion will almost certainly void their warranty.

  7. charlie_sullivan | | #7

    If you want to make good use of the hydronic tubing, I would consider a chiltrix, to supply that tubing and also supply a few of their nice sleek fan coil inits to use instead some or all minisplit heads.

    Otherwise, it depends what your objective is as far as backup heat. If it's really only for if your minisplits break, then electric resistance heat seems fine.

    Are you also asking about domestic hot water heating, or only supplying the floor? An inexpensive and quiet way to cut dhw energy is a drain water heat exchanger.

  8. Jon_R | | #8

    Maybe someday someone like Fujitsu will make a hydronic indoor unit to match their popular outdoor units and sell it in the US.

  9. BrandonA | | #9

    Sorry I was posting shortened links because the actual links were crazy long and distracting, now I know better I guess.

    Thanks for everyone's input, I really do appreciate it. I was hoping for the Chiltrix to supply DHW as well as radiant heating since my loads are soo small. However it appears to do that I will have to use an indirect water tank. I was really set on the Marathon as I like the idea of NEVER having to replace the tank or worry about a leak. The indirect tanks are stainless steel for the most part and might not last long from the effects of chlorinated water, not to mention they are more money with less capacity.

    I may end up with a few multi head mini splits (for zoning) and a resistance water heater. Hopefully my PV system will cover the extra energy usage of a 105 gal. resistance water heater that I can use for low temp radiant as well.

  10. charlie_sullivan | | #10

    In principle, one could certainly buy an external heat exchanger for a few hundred dollars to enable using a marathon tank with a chiltrix as a heat source. You'd need an additional pump to circulate the DHW from the tank through the heat exchanger, and you'd need a controller that would interface with the chiltrix and with that pump. This is where Martin rolls his eyes at the fact that I, as an engineer, tend to propose overly complex systems, and he is most certainly correct about that.

    But the "simple" solution, of a marathon supplying both with its electric resistance heat, should also have a heat exchanger to separate the DHW from the floor loop.

  11. BrandonS | | #11

    I didn't see a mention in your original post. Have you seen the Arctic heat pumps? The 29,000 BTU model goes for $3,382.

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