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Community and Q&A

New Air to Water Heat Pumps on the Horizon

Nick Defabrizio | Posted in Mechanicals on

I have an oil boiler/hot water baseboard system as the initial heat source.  I then installed two 12kBTU Fujitsu low temp mini splits in the main part of the house and tonight (9F) they are doing fine. I am planning to finalize the switch to all electric soon. However, I must admit I like baseboard heat a little bit more than hot air heat.  It made me think about Air to Water (A2W) heat pumps.

As most of you know, the problem with A2W systems to date is that the water temps they produce (e.g., 110-120F) will not work well with existing residential baseboard systems designed for 180F boilers. But recently I was speaking with The Radiant Store in Troy NY and they mentioned that there are new systems rumored to be out in the near future that may be high output. Then today I  saw an article about an A2W heat pump developed by Feenstra/VattenFall in the EU that is purported to deliver 160-180 water using C02 and a big buffer tank.

Obviously a plug and play A2W unit that works with my existing baseboard would be a game changer for me and many others who have baseboard. I am wondering if anyone has any further knowledge about this system (or other A2W systems that might be on the horizon) and when  we might see interesting new developments in this area….either in high temp units or some other advancement in these systems…

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  1. DCContrarian | | #1

    Interestingly enough, this was in my in-box today:
    "f you were interested in SpacePak but were concerned about whether the units would work in your colder climate, we've got good news for you: The new Solstice Split Inverter system is able to provide both heating and cooling in climates that get as low as -20f."

    The link is:

    I know nothing about it, just forwarding what I received. It does sound interesting.

    1. Nick Defabrizio | | #2

      Yes thanks. These seem to be nice units that probably borrow technology from Air to Air low temp split systems; then marry it to a water heating unit in a monobloc design. I think because they are R-410 based, they top out around 120F, effectively eliminating the plug and play aspect for existing baseboard systems designed for 160-180F water temps. The online seminar they offered in February seems interesting and may portend future models with higher working temps, however.

      For folks designing new systems, the 120F systems seem to work well with radiant in floor, low temp radiators, FCU's or even high efficiency baseboard like the Smith H-2 models that put out almost 400 btu's per foot at 120F. They also provide cooling through FCU's. Certainly something to consider along with or in competition with forced air systems. It seems hard to compare ultimate efficiency on some of these though.

  2. Charlie Sullivan | | #3

    What I did was to add some panel radiators to supplement my baseboards and run them all at low temperature. Combined with some envelope improvements that's worked great--I rarely have to raise my water temperature above about 95 F. You can also consider floor or ceiling radiant heating where that's easy to add for effective heating without high temperatures.

  3. John Iskander | | #4

    Hi Nick, Thanks for letting us know about this. It is absolutely what I am looking for as well, albeit full radiators, not baseboard heat. I wish it were here already, and from what they are saying it will 'be rolled out later this year' meaning it is not present even in the Netherlands, much less the UK which they see as their next market. Somebody has to be planning one of these for the US market?! I'm not urgently in the market for this right now, as the old gas boiler continues to plod along, but wow, I am ready for this! Link below to the announcement from Vattenfall.

    1. Charlie Sullivan | | #5

      There are some that can get you to 130-140 F, which might be enough if you also do some improvement of the envelope, and maybe adding a few extra emitters. For example,

      1. John Iskander | | #7

        Thank you! This looks interesting, sure enough.

  4. seanm10660 | | #6

    I also would love to swap out my aging gas boiler for an air-to-water heat pump. I've had my eye on the European R32-based A2W systems like the LG Therma V. These seem to be able to generate higher water temperatures at lower air temperatures, compared to their R410 systems. LG's newest "Monobloc S" can make 130F water down to 5F maintaining 95% rated capacity, which seems pretty good.
    Most of my baseboard is oversized for the current heat load, and I've calculated that I can lower my water temperature pretty far (in most rooms), though 130F at my coldest outdoor temperatures (design ~8F) might be tight.
    I'd love to see more of these C02 based heat pumps enter the market, though!

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