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Seeking an air-to-water heat pump

Allison Ashcroft | Posted in Mechanicals on

I’m looking for an air-to-water heat pump and feedback from those who’ve used them. We have a LEED for Homes project in Victoria, BC, perfect climate for heat pump, affordability of project prohibits groundsource for 36Kbtu heat loss of 1800 ft2 home and for optimal comfort, low temp/efficiency, to avoid ducting we’re selected hydronic in-slab for heating distribution thus standard air-to-air heat pump is a no-go. Can anyone suggest an air2water heat pump they’ve seen or used and can anyone provide feedback on their experiences with it particularly if you’re in BC/Wash/Oregon where climate is similar and relevancy is heating dominant.

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  1. GBA Editor
    Martin Holladay | | #1

    Most air-to-water heat pumps are made for producing domestic hot water, not space heating. Among those manufacturing such units are General Electric, Rheem, and AirGenerate.

  2. Andrew Henry | | #2

    Hallowell is working on a air-to-water for hydronics.

    And I think I remember reading that Mitsubishi might have something ready.

    As recommendation, put lots of styrofoam under the slab, at least R20.

    Finally, having spent a couple of weeks in March, a couple of years ago, I couldn't help thinking that homes built to the Passive House standard would be pretty easy to achieve there.

    Good luck with your project.

  3. Andrew Henry | | #3


    That should have read "having spent a couple of weeks in Victoria in March".

    Also I checked and the Mitsubishi heat pump I was thinking of is an air-to-air.

    If you are going for LEED you may want to consider how efficiently you distribute the hydronic heat around the house. There are a few really efficient circulators from Europe that are starting to be available here.

    The Wilo ECO Stratos is an A rated variable speed circulator that I found made my hydronic system easier to design. It also helps to eliminate some hardware, specifically a differential pressure bypass valve. Which was something I couldn't get my head around!

    Here's a little more info on what a system using a EC motor variable speed circulator would look like.

    Just substitute the air-to-water heat pump you are planning to use for the ground source one in the diagram.

    Grundfos also makes an EC motor variable speed circulator, I believe it's called the Alpha.



  4. Anonymous | | #4

    In the US you may also want to check out RC (reverse cycle chiller) units from Unico (Unichiller RC), Aqua Products, and Multiaqua....

    In Canada; Aermec (from Italy) is currently being distributed ....

    There are a number of manufacturers that could enter the North American market with Asian and European products; Daikin, Hitachi , Mitsubishi, Sanyo, Stiebel Eltron, Veissman etc.... of course pending getting UL/ETL certification for North America...

  5. stan | | #5

    Look Daikin Altherm. It is specifically made to provide hydronic water heating and domestic water heating for residential. If you find something for commercial I would appreciate some feedback.

  6. Nom DePlume | | #6

    For US and Canadian readers;

    also has a link to Daikin Altherma technical info in “American Units” instead of SI Units;

  7. Aj Builder, Upstate NY Zone 6a | | #7

    So glad I found this posting. Thank you all for the info.

    Please update this as anyone sees more news.

  8. John Semmelhack | | #8

    The Daikin website now has info. on the Altherma. Go to

  9. GBA Editor
    Martin Holladay | | #9

    There's more information on the Altherma here:
    A 'Magic Box' for Your Passivhaus

  10. Aj Builder, Upstate NY Zone 6a | | #10

    Still looks like October for first ability to purchase?

  11. Kevin Dickson, MSME | | #11

    The Geyser for DHW, maybe more...

  12. Mike O'Brien | | #12

    First Daikin Altherma system installed in Portland looks good, however, I got a quote of $22,000 to install a system in our house, and because it is not yet elegible for the 30% Federal renewables tax credit, it's an expensive way to reduce electric energy use. I have to say I don't understand where the high price comes from, the components are pretty straightforward to install.

  13. Bill P | | #13

    I have priced out the Mitsubishi Zuba Central for our 1,110 sqft raised brick bungalow. It came in at about $11,000 including new water heater. Good price and competitive with the FAG systems I was quoted. Now comes the debating... I have searched and only found a couple reviews that were positive but no concrete numbers for what was paid yearly on heating/cooling.

  14. Tim Dobson | | #14

    I discussed with Mitsubishi the last 2 years, a air2water heat pump system for hydronic heating and cooling. They have a larger 6 Ton City Multi model for commercial use just introduced. they expect to have a smaller 3 ton air2water unit ready for test instalations by december 2010. I expect the full role out for spring 2011 for the AC season. Efficiency is apparently 378% range. Pricing will be fair as the install labour is easy. wait a bit. I am.

  15. Anonymous | | #15

    I'm looking for a unit that is about 12000 btu/h ... the geyser is 6000 btu/h (is that an outdoor unit?) ... the altherma is 38000 ... unichiller is 30000 or so ... seems like a gap in the range for all the ones I've seen. Any help or direction? Thanks.

  16. Michael Chandler | | #16

    I was judging the DOE Energy Value housing awards last week and there was a guy in the pacific northwest who was using a UniChiller for heating radiant floor as well as domestic HW on a project. it was a very well-built home (Not worth applying for an EVHA award unless you've got an excellent project cause the competition is brutal) so he had a great insulation package but the price was affordable for the project overall and the system was very elegantly engineered.

    Unichiller in general is pushing their high velocity HVAC systems so this is the first time I've seen someone use just the heat pump part for heating water for radiant. Theoretically you could use it for cooling but that would involve air handlers etc. From what I see it looks to be less expensive than the Altherma and they have good distribution in the US.

    The Geyser is a domestic water heater that must be installed in a space that doesn't drop below 40 degrees and issheltered from the weather. Not likely to be much use for radiant heat unless you live in a pretty warm climate. 6,000 BTHh is tiny, by comparison a Rinnai tankless water heater typically modulates from 15,000 to 199,000 BTUh so it's lowest setting is 2X the Geyser...

  17. Kevin Dickson, MSME | | #17


    6000 Btuh is average for a HPWH. Of course, they all use storage tanks, so a comparison with a tankless is meaningless.

    You're right, the Geyser was never designed for space heating, and all air to water heat pumps have issues with ambient temperatures at the evaporator.

    For a discussion of the issue, see:

    Follow this link to see why a well-insulated garage could be the best place for a HPWH:

  18. Anonymous | | #18

    I talked with the people at Geyser and they said someone is trying it out for hydronic radiant heat in a small super well insulated space as well as domestic hot water where they have a marathon electric hot water tank to supplement. I'm planning a similar setup and am pretty convinced that 6000 btu/h would be just enough to meet my needs for my 1000 sq ft well insulated, passive solar house in WA. Plus the thing is only $1000. The killer for me is that it has to be indoors.

    I'm talking with the people at CIAT too regarding their Yuna 20H model -

    That model is about 18,000 btu/h and is due to be ready this month. No word on price yet. This is overkill for me but might be the smallest outdoor model on the market. I don't really want to oversize my heat pump for many reasons ... smaller is quieter, cheaper to buy and cheaper to operate. Wish I could find an option in the 10,000 btu/h range that could be installed outdoors.

  19. Anonymous | | #19

    After further discussions with CIAT I found out that their heat pump is designed for 50Hz ... which is the European standard.

    Why is there no small sized air to water heat pump available on the US market? I don't need air conditioning - just heating and I live in a climate where the temp rarely drops below 30 F and never drops below 0 F.

    Someone must be making such a product ...

  20. Ted Herford | | #20

    I have found and air to water heat pump from Techwell industries in Hong Kong, China. It is a DC inverter heat pump. It is a split system, an outdoor unit and an indoor unit. It will supply hot water for radiant floor heat and domestic hot water. The unit I want to purchase is $2100 plus shipping to Vancouver, Ca ($200) . It is a 3 ton unit (36000 btu/hr). I don't have experience with this product yet, but believe it is the way to go for my project. Purchasing a product from a Chinese company may be offensive to some, but I have yet to find an affordable product produced in the U.S ($6000 and up). There are several products produced by toshiba, mitsubishi etc. that are I am sure are great products that have been built for the European market and not yet available for the US and the ones that are availble such as Daikin are cost prohibitive (over $10000). Aqua products in South Carolina builds an air to water heat pump in conjunction with York but I found their customer service to be very unresponsive to my email inqiries and I finally found out the price of their product ($8000) from a dealer. Since I am looking for a DC inverter heat pump that is more efficient one is forced to look outside the US for a product.

  21. Murray Hasick | | #21

    There are two distinct categories of systems available for air to water applications. The first are for domestic hot water generation - either integrated with a tank - GE,Rheem - or separate units tied in with an existing electric tank - Geyser, Air Trap. The second category of systems is for heaitng and cooling via radiant floor or fan coil on the heating side, or fan coil on the chilled water (cooling side). The latter category ranges in sizes from 3 tons up to 5 or 6 ton capacity. As mentioend Daiken, Unichiller and Aermec are currrently in the developing market stage. However, there is an entirely US made system - NorAire - out of Minnesota (Electro Industries). The NorAire system has incorporated some significant advantages over the other market palyers especially on the back up heating side, and the defrost cycle which is very important in colder climates. NorAire has a design manual which I have attached.
    The air to water systems are especially adept at radiant floor heating, as they produce a lower supply water temperature - 105 to 110 F. They can also be used to pre-heat a domestic hot water tank in the same way that a ground source heat pump does. In fact, it may be reasonable to think of an air to water heat pump as a poor mans geothermal system. Same result, but with slighty lower performance (dependant on ambient temperature conditions). However, installed cost is going to be about 1/5 th that of a geothermal system.
    There are currently no third party ratings for air to water systems - AHRI - who rate air to air and other HVAC equipment, so be careful of claimed COPs by some air to water manufacturers. However, it is likely the performace is going to be in the range of 1.5 to 2 - better than a gas boiler at 95% AFUE, plus you get cooling.

  22. Aj Builder, Upstate NY Zone 6a | | #22

    Nice to see the last two posts. I bet there is a sizable market for low cost heat pumps that are reliable and that a suitable for colder climates too.

    Murray, page 4 of your PDF looks like a nice system that would cost $35,000 is my guess. Am I close?

    Ted, I hope you update us, nice post, great cost for the HP part of your HVAC system.

  23. Murray Hasick | | #23

    More details on the NorAire system have been added to thier web site at
    Since there are a myriad of system configurations, the pricing will range significantly from a basic single zone heat only radiant system to a multizone heating and cooling application. While the air to water was primarily targeted for radint floor, the chilled water capability opens up some options on the cooling side - central fan coil or individual room units (buffer tank required). A basic system with heat only one zone of in-floor will have an equipment cost about the same as an air to air heat pump.
    Where the air to water systems will shine, will be in areas with moderate winter temps - Pacific Northwest, etc and as a miuch cheaper alternative to ground source equipment - no field loops, pumping eqpt, well drilling, etc and producing exaclty the same water temperature.
    As far as inexpensive offshore equipment goes, buyer beware. Two of the major offshore players in the market right now are nowhere near the cost that one of the previous contributors quoted. There are hundreds of Chinese, Taiwanese and Korean system out there, but if you buy one, who is going to support it after sales? Unless you are a refrigeration mechanic that can trouble shoot your purchase if need be, good luck.

  24. Ted Herford | | #24

    Hi all,
    I did the post on purchasing an air to water heat pump from a Chinese manufacturer. I continued to research this option after my posting. Even though I felt the Chinese product was the answer for my radiant floor system, I decided not to purchase the equipment for the reasons stated by another person on this post, which was what would I do when it came time to service or replace parts. I felt my options would be very limited, if any. I ended up buying a used 3 Ton Unichiller RC (3 years old) that I found on Craigs list for around a 1/4 or less of the cost of a new one. The Unichiller design does not require a refrigeration tech to install since the refridgeration cycle is contained in the unit itself. All I had to do was plumb the water from the unit to my radiant floor and hook up the power. My Taco zone controller has an end switch that starts the Unichiller whenever heat is called for. The Unichiller is providing 115 to 120 degree water, which is fine for my radiant floor. I also plumbed a heat exchanger in the the radiant loop that preheats the water going into my domestic hot water tank which should also reduce the cost of my domestic hot water needs. The only other thing I am going to do is obtain a thermostat switch that will turn the water pump on in the unichiller whenever the outside air temp gets to 35 degrees or lower to prevent my water loop from freezing. I am now waiting for my next electric bill to see what the savings will be . All is well in Bellingham.

  25. David Meiland | | #25

    Ted, greetings from Friday Harbor and thanks for the update. I would be very interested in how this performs and what the operating costs are, as you move forward.

  26. Aj Builder, Upstate NY Zone 6a | | #26

    Ted, updates?

    Andrew, examples of system sizes and complete installed costs?

  27. Andrew Young | | #27

    Right now we only have to models with NRTL certification for sale in Canada and US. The two models are 2.5 ton and 4 ton. They are rated for heating operation to -15degC but I have had them working below that.
    I am not an installing contractor, just the distributor. Through contractors I work with, we advertise an installed cost for the 4 ton model at $9,500. This is if you are adding to an existing infloor radiant system. This includes the heat pump, storage tank, water to glycol heat exchanger, pumps, glycol, all associated piping and wiring and installation. The electric or oil furnace has to stay in operation for back up heat.
    For larger installations it is very easy and inexpensive to double up on the heat pumps. I just completed an install in a 7,500 sqft home (not including the basement) that was built in 1850 and we used 2 heat pumps. In this install we are preheating the domestic hot water as well we have a forced air system for air conditioning.

  28. Andrew Young | | #28

    I am the Canadian Distributor for a line of Air to water heat pumps. We have many installed with fantastic results. or [email protected]
    We offer sales as well as technical support for your systems.

  29. Stepan Klymenko | | #29

    I am very glad to found your discussion about Air-to-Water Heat Pumps for United States.

    I live in Chicago and would like to install such heating/cooling system myself.

    Seems like Daikin Altherma is the only system available in USA. But, Europe has much wider selection, systems like Panasonic AQUAREA, LG Therma V and others.

    Can someone help me figure out, what I can install, as of 2014, for heating/cooling from Air-to-Water Heat Pumps

  30. GBA Editor
    Martin Holladay | | #30

    Q. "Can someone help me figure out, what I can install, as of 2014, for heating/cooling from air-to-water heat pumps?"

    A. I think that you have answered your own question; the answer is the Daikin Altherma. That said, for space heating you should consider the use of ductless or ducted minisplit units instead of an air-to-water approach. You'll save a lot of money if you take this advice.

  31. Expert Member
    Dana Dorsett | | #31

    One reason the offerings for hydronic output heat pumps in the US are much fewer than in Europe is that air conditioning loads (particularly the latent loads) are much higher, at least in most of the US. While chilled water coils can also be served with hydronic output heat pumps, it's an additional expense.

    The other reason is the performance of most hydronic output heat pumps is pretty abyssmal at US zone 5 or colder outside design temps. In Europe the Altherma is the performance leader in Scandinavian climates, according to independent testing done in Sweden a few years back. (If I could recall enough Swedish I could probably google it up some comparative efficiency documentation for you, but my grasp of the Nordic lanquages are a bit weak, even though I can read it with sufficient comprehension to get the gist of it.) Northern Sweden's outside design temps are comparable to a US zone 6 climate. Most of northern Europe is closer to US climate zone 4, from a 99th percentile outside design temp point of view, which is a lower hurdle for air source heat pumps to work with, but those same areas have extremely modest cooling requirements compared to US zone 4A & 4B.

  32. Nick DeFabrizio | | #32

    I would like to revive this thread for a second. For retrofits, geothermal systems are often too expensive due to the cost of vertical drilling and horizontal trenching. Also, retro fitting radiant systems is expensive, and ductwork is often inefficient. Recently I stumbled upon the web site of Thermomatrix in BC, Canada ( Not only do they sell a relatively inexpensive Air to Water HP ("Cool Fire"), but they also sell a " fan coil, forced convection ductless air distribution system" called "Comfort Coil" which seems to be a hybrid between a ductless system and hydronic. I am curious if anyone has experience with these products or similar products?

  33. Daryl Ross | | #33

    NICK DEFABRIZIO: Where did you get with Thermomatirx? I'm also looking at their systems...

  34. Ted Herford | | #34

    I to am looking for an air to water heat pump product for my home in Bellingham Wa. I purchased a used 3 ton Unichiller about 3 years ago and while it has done the job to some degree it just does not produce enough btus/ hr. Below 30 degrees to keep up with the heat demands of my home. I checked out the Thermomatrix product. The 5 ton unit would give me the btus I need, but they achieve it by using two compressors. When are North American companies going to catch up with the current refrigeration technology being used by foreign manufacturers (China,Japan,Europe etc.). I am holding out for a DC inverter style system with EVI ( enhanced vapor injection) technology. The inverter style compressor is much more energy efficient and the EVI technology enables the heat pump to produce heat at lower temperatures. Since I am looking at this from a lay mans viewpoint I imagine there are HVAC techs that
    Will not agree with me; however, they will have to come up with some pretty convincing arguments to sway my opinion. There are a lot of inverter heat pumps for mini split ductless systems (foreign built) but not for hydronics. Perhaps the market for hydronic systems is not large enough. I again have found a product by Macon in China that meets my requirements. China has a huge vested interest in HVAC
    Products because their air pollution problem is severe and they are looking at hvac systems as one of their solutions to reducing their carbon footprint. This says to me that their goal is to produce quality equipment. I am currently looking for an import broker that could handle my purchase. It seems they are not interested in the individual looking to make a single purchase. I continue to look for a product that I could buy here. So far Mitsubishi may have what I need.

  35. Molly Schwarz | | #35


    I also have a need similar to yours. What is the mitsubishi you reference? And are you able to purchase it in the U.S.?

  36. Murray Hasick | | #36

    As of November 1 2014 I'd like to update my take on the air to water market. First of all I represent a line of air to water systems in W. Canada manufactured by Gree China. If you look at the world market for air to water, statistics published in the Japanese Air Conditioning Refrigeration News for 2012 showed the following - China 890K systems, Japan 400K systems, Europe 250K systems and N. America fewer than 1000 systems across all manufacturers. So the investment by a major manufacturer to get certifications etc for N America is based on that small number of systems being installed. The air to water market is a small subset of the hydronic heating market which in itself is 6% of all heating systems installed in the N. American market. Having said that, the quality manufacturers are trying to grow the air to water market here. It is a great option to ground source systems in areas like the Pacific Northwest at a much lower installed cost. There are some good options out there - just don't expect bargain basement prices for the quality, inverter based systems.

  37. Charlie Sullivan | | #37

    I just tried to find the Gree products on their web site, and couldn't figure out how to find air-to-water systems. Can you point us to them?

    My opinion on the whole topic: I suspect that there's a higher incidence of leaks and accidental refrigerant releases from minisplits than from hydronic units that are factory charged. So I think a packaged hydronic unit is a better approach.

    Also, there are endless discussions here about how well the heat from a minisplit is going to get distributed to various rooms. Adding a radiator or fan coil is no big deal with a hydronic system, so that becomes a non-issue.

  38. GBA Editor
    Martin Holladay | | #38

    Murray and Charlie,
    In theory, the advantages of hydronic distribution of space heat are obvious. The main stumbling block to this idea -- one that the Altherma systems have long faced -- is high cost.

    If a manufacturer can deliver high quality and low costs, this idea has traction. Otherwise, air to air space heating systems will continue to dominate.

  39. Blake Klopfenstein | | #39

    I would like to revise this conversation regarding Air to Water heat pumps. I'm currently building a new 2600sqft home on Vancouver Island, British Columbia,Canada and we're planning on installing concrete floors for indoor hydronic heat. Because of our higher than normal year round air temperature and absence of natural gas in our region, heat pumps seem to be the most practical solution for space heat and domestic hotwater. We have corresponded with the Thermo Matrix company in Kelowna as the have 3 ton mini split air to water heat pump systems that space heat and provide domestic hot water as well. As these systems are new, there is little for reviews on these systems. However, they have been documented on being used in the Miidori Uchi design built by Naikoon Contracting in North Vancouver with success.

    If anyone has experience with these specific units or competitive equivalents offered for purchase in western Canada any further input would be appreciated. Thermo Matrix had quoted approximately $7000 for the 3 ton mini split, but I'm assuming install would be extra.

  40. Murray Hasick | | #40

    The Gree System uses inverter compressor technology vs the on/off compressor in ThermoMatrix and is comparable to the Daiken Altherma Split system at a 15-20% reduced cost. The product is sold via Certified contractors trained on the product line to ensure quality installations. I am happy to field any questions at [email protected]

  41. Kevin Caldwell | | #41

    This is pretty late to the party, but I thought I'd share my experience with an air to water heat pump. I have been using a Unico Unichller 036 for 11 years now, in a hydronic floor heated 1,800 sq. ft. house on Vancouver Island, near Courtenay. I installed the whole system myself, using a hot water tank for indoor water storage. I also use the hot water tank heaters as a back-up system.

    The house was built for very low heat loss: SIP panel construction including the roof, heat mirror windows, thorough sealing, etc. The Unichiller has provided more than adequate heat, and our average winter heating bill has been below $300 consistently. We do not have natural gas service, so electric is about our only heating option.

    Our Unichiller was a very early unit, basically a hand wired prototype with only a defrost board and sheet metal mounted relays. The relays and wiring have given some issues, the defrost board died, and two refrigerant pipes rubbed against each other until they wore through and started to leak. It has required a certain amount of attention. But it has been an economical way to heat a house.

    We are presently researching Chinese units as a replacement as the Unichiller is getting old - hopefully it has a few more years left in it. The Chinese HP are much lower priced than the few available in North America. Some of the Chinese units seem to have good performance. Replacement control boards are available on AliExpress, etc.

  42. GBA Editor
    Martin Holladay | | #42

    If you are considering purchasing a Chinese air-to-water heat pump, you might want to read this article: Air-to-Water Heat Pumps.

    In the article, I discuss two Chinese air-to-water heat pumps: the Chiltrix and the SpacePak Solstice Extreme.

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