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Recommendations for a High-Temp Air-Source Heat Pump

greenskies | Posted in Mechanicals on

I’m looking for a hight-temp (140-160F) air-source heat pump. I have reached out to many contractors and none have been able to provide an alternatives to the LG Therma V or Daikin Altherma that is available in the Lower 48 United States.

Do you know of one?

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  1. Expert Member
    Dana Dorsett | | #1

    Sanden's CO2 refrigerant water heaters are capable of delivering 176F water even when it's -20F outside, but capacity and efficiency are better if running cooler water than that. They're nominally rated 4.5 kw (= 15,000 BTU/hr) output, which is enough to heat a low load home.

    The NEEA utility consortium in the Pacific Northwest is currently testing eight 2.25 ton (28,000 BTU/hr) combi-heater applications based on Sanden technology, briefly outlined on page 3 of this document:

    ...which was a follow-on to the prior testing mentioned here:

    See also:

    In France they already sell hydronic Sanden combi-heater units using the same compressors with similar capacity to their water heater, but haven't seen it in the US yet. There is at least one PassiveHouse in Portland OR that I'm aware of using a self-designed combi system based on the water heater.

    1. greenskies | | #2

      Thanks for the reply!

      Is sizing a system like this comparable to an oil furnace? i.e. If my oil furnace is 140k BTU, would I need 10 of Sanden's CO2 refrigerant water heaters or 5 of the 28ks?

      Or does the 3.84 energy factor make 1 15k equivalent to a single 72k 80% efficient oil furnace?

      1. Expert Member
        Dana Dorsett | | #4

        If your oil furnace is 140KBTU (either input or output), it's most likely ridiculously oversized for your house, assuming your house isn't 8-10,000 square feet or completely uninsulated with a couple of windows missing glass.

        To figure out what is really needed to heat the place, run a fuel use based load calculation to put a firm stake in the ground:

        Most 140KBTU heating systems in the use are at least 3x oversized for the 99% heating load. If the radiation is similarly oversized the actual space heating load it can be heated with 115F water instead of 160F water.

        Given the high up front cost and potential efficiency hit of oversizing heat pumps, it's important to have the load numbers nailed down pretty accurately before specifying the system to meet that load. The 15KBTU Sanden water heater compressor unit (no tank) costs about 2 grand, installed in a system it would likely be closer to four grand, not counting the costs of the other system components.

        The Sanden needs a very high in to out temperature difference and low entering water temps to run efficiently. When using it for a space heating combi system the system design can make or break it. Yes it can deliver high temperatures, when there is a high temperature output and/or a small temperature difference a simplified hack system might not even be as efficient as an electric boiler. It's not nearly as simple to design with as hydronic boilers.

        The term "furnace" in the US HVAC world normally refers to ducted hot air space heating, but the Altherma and LG Therma V are hot water. Is what you're calling a "furnace" really a "boiler"? In most US dialects they are not interchangeable terms, though in some parts of the mid-Atlantic region they seem to be.

  2. this_page_left_blank | | #3

    The energy factor is a measure of power in vs power out. The 15kBTU rating is output, so the energy factor is not relevant. Unless your home is more like a palace than a house, it's unlikely that you really need 140kBTU. Ten SanCO2 water heaters would run you in excess of $50,000 once you factor in installation.

    1. Expert Member
      Dana Dorsett | | #5

      Mitsubishi has commercial CO2 refrigerant water heating systems that can probably come in well under $50K for a 100, 000 BTU/hr system, but it would be silly to go there if the actual load is 25,000 BTU/hr. Run a web search on "Q-TON "

      Most homes don't have the 3 phase power needed to run one though.

  3. denntl01 | | #6

    Have you found a response for you air source heat pump?

  4. kieran973 | | #7

    Does anyone know why the LG Therma V is not for sale in the US? It looks great - I don't understand why there seems to be no market (or installation/service network) for it here.

    1. Expert Member
      Dana Dorsett | | #8

      >"Does anyone know why the LG Therma V is not for sale in the US?"


      The market for hydronic heat pumps in the US is simply smaller than in Europe, largely because the paradigm for heating in the US is ducted hot air, in part to make it easy to use in combination with air conditioning.

      There are other monobloc style low-temp hydronic output systems already in the North American Market (Arctic, SpacePak, Chiltrix) but very few split systems. The Therma-V comes in both monobloc and split versions. The max output temp of the Therma V is a fairly modest 65C/149F, but the capacity and efficiency at that temp probably isn't all that great. Split systems are preferable to monoblocs in locations that can go weeks without breaking the freezing mark, avoiding the need for antifreeze in the system.

      LG's Multi-Vs full-on VRF system is available in the US, and there are both low-temp and higher temp HydroKit options available that will work with 4 ton versions (and some mu. The Multi-V works with most of their wall coils and air handlers for the air conditioning part, and with a "reverse indirect" as the hydronic heating system buffer it can deliver domestic hot water at reasonable temps and reasonable efficiency.

      The 4 (& 5 & 6) ton Multi Vs is also now available in a version using (more climate-friendly) R32 rather than R410A too. The global warming potential of R32 is roughly 1/4 that of R410A. I'm not sure if they have updated R32 Hydro Kits though.

      The full VRF system is capable of simultaneously heating some zones and cooling others, which means in summer it can potentially heat the domestic hot water with the heat it's pulling from the house at VERY high efficiency, which is using the house as something like an oddly shaped solar collector.

  5. kieran973 | | #9

    Hi Dana,
    Thanks for your detailed reply. I've read a lot of your stuff on GBA (and I read an interview you did about minisplits somewhere too) so I've been learning a lot from you in general.

    Do any of these air to water heat pumps work with cast iron radiators? If so, how complicated is the installation? Is it just a matter of swapping out the old boiler, swapping in the new heat pump and buffer tank, and maybe doing some minor re-piping? Or is it much more elegant/complicated/expensive than that? The reason I'm asking is because I have extremely oversized radiators in three upstairs bedrooms. These radiators are 5 ft long by two ft tall, inside bedrooms that are only 100-150 sq ft. I've been working on a Manual J heat load for my house using Cool Calc, and the latest working number is around 47,400 BTU/hr. Assuming the upstairs of my house is roughly 1/3 of the heat load (the upstairs is around 500 sq ft while the downstairs is around 1,000 sq ft), then according to this chart below as well as some of my own napkin math that I'll spare you here, my cast irons should be able to meet the heating loads of the bedrooms at temperatures as low as 105F.

    The radiators are supplied by a natural gas boiler at the moment, but I want to replace the whole house heating system with a heat pump. I was in the process of getting quotes for Mitsubishi hyper heat minisplits when I learned about air to water heat pumps (Arctic, Chiltrix, etc). If possible, I'd like to keep the cast iron radiators -- it would be a shame to throw out something that's been in this house for almost 100 years (built in 1925), plus before moving in to this house, I lived in NYC area apartments for most of the last 15 years and I much prefer radiator heat to the dryness of forced hot air. But I can't seem to find any info online about concrete examples of air to water heat pumps working with cast iron radiators. I'm getting the sense that the smarter move may be to just go back to pursuing ductless minisplits....

    1. Expert Member
      NICK KEENAN | | #10

      The beauty of hydronics is that the radiators don't care how the water got heated, you can mix and match.

      The only thing you might worry about is that heat pump are more sensitive to clogging than boilers, I know Chiltrix recommends a filter on the return side. Hundred year old radiators probably have a lot of crud inside, and a lot will shake loose when you open the system. A normal filter might clog and cause problems, you probably want a jumbo filter on the return.

      The easy way to see if your radiators can warm the house with water at 105f is to turn down your current boiler and see how it does on a cold day. You'd have to wait for next winter.

      1. kieran973 | | #11

        All good points. And just more reason to stick with plan A, which was air source ductless minisplits. Thanks.

  6. Expert Member
    Dana Dorsett | | #12

    To know if it will work at low temp requires measuring or calculating the heat load, and measuring the size of the radiation.

    A pretty good overview of what was available in the US (and Yurp) as of a couple years ago, as well as some of the design issues were presented by (well known hydronic designer & author) John Seigenthaler to an audience of hydronic heating nerds at a Massachusetts Clean Energy Center conference a couple of years ago, captured in these videos:

    (Yes, these are on the long side, but packed with a lot of detail.)

    1. Deleted | | #19


  7. CatherineLiz | | #13

    Dana, I am writing to follow up on your very helpful posts here and elsewhere on this site. I am a first-time home builder (that is, having a home built for the first time) in Central New York. I would like to heat and cool the house using an air to water heat pump, heating through in-floor (staple up) radiant heat and cooling through ductless mini splits. A local HVAC contractor is recommending the LG Hydro Kit. I am very intrigued by this technology, particularly given what you have written about it.

    I have three concerns:

    1. It uses the R-410A refrigerant, which is being phased out. Let's say I need a new refrigerant for some reason in five years and R-410A is no longer available. Will I be in trouble or do you anticipate there will be alternatives?

    2. LG quality. My research so far suggests that Mitsubishi and Fujitsu are preferred in the air source heat pump category and that LG is mid range quality. Do I need to worry about the reliability and longevity of an LG unit?

    3. Suitability for residential. Are the smaller Hydro Kits indeed suitable for small residential units (1,700 square feet)?

    If you, Dana, or any others have insights that you might be willing to share I would be very grateful. I have been researching options for months and have only come up with this LG Hydro Kit or a ground source heat pump.

    I should note that I have spoken with folks who have had great luck with Arctic and mixed luck with Chiltrix, however I have not found anyone local who will install and service these.


    1. paul_wiedefeld | | #14

      Hi Catherine - I think you’ll find most advice will steer you away from a radiant floor, regardless of heat source, especially since you’re intending to install AC. Basically, you’re spending an extra $20k+ for floors that won’t be much warmer than room temp, plus adding an exotic, unnecessary heating system for a house that’s smaller than the average new house. Air to water heat pumps aren’t common place as you’ve seen and ductless systems have their own limitations. Getting a ducted, air-source (not geothermal) heat pump and spending a bit more on air sealing/insulation/solar gets you lower bills and probably better comfort, cheaper.

  8. CatherineLiz | | #15

    Thank you very much for your prompt and helpful reply, Paul. And please forgive me. I recall seeing quite a bit of advice *against* in floor radiant heat on this site. I've gotten confused going down so many rabbit holes that I forgot...

    I had remained focused on radiant because a) folks who have it around here absolutely love it, and b) it is common in Europe and I tend to assume they are usually about a decade ahead of us.

    But your advice is well taken and I will pursue it. In this case, is there any advice on LG vs Mitsubishi? I don't see LG getting as much attention on these pages as Mitsubishi, Fujitsu, etc, and the refrigerant experts with whom I have spoken prefer Mitsubishi. I certainly welcome any advice this forum has and I'll also continue to explore the various fora.

    Thank you again. This community has been incredibly instructive.

    1. paul_wiedefeld | | #16

      Ha don't worry about Europe. AC is less common. If you're getting AC, it's redundant. If that $20k+ is worth it, I'd still install ducted for AC and heat as backup.

      LG has the Hydrokit so that's your air-to-water option. I don't know how reliable that is or isn't, but the entire radiant system is much more complex (which is why they make little sense for new, smaller homes). You'll need at least two circulators, buffer tank (possibly), expansion tank, auto feeder, antifreeze, dirt/air filters, a manifold, valves/more circulators (controlled by multiple thermostats), outdoor reset etc. None of those parts are needed for a ducted system. None are cheap.

      If you're doing ducted heat pump, really any manufacturer works. The installer is more important. LG, Mitsubishi and Fujitsu have cold climate options, but installing a well-sized modulating heat pump with electric resistance is a great choice too.

  9. CatherineLiz | | #17

    Paul, thank you. I think this has finally convinced me to let go of the radiant option.

    I am a university professor and this week in my nonprofit management class we discussed the concept of “new power,” which among other things suggests that communities rather than single elite institutions productively wield the power of the future. This GBA community has certainly helped me sift through the advice of local HVAC contractors who has their own interests at stake. Thank you again.

    1. paul_wiedefeld | | #18

      Glad I could help - that concept seems to especially apply to climate change and the energy transition. There are experts for sure, but a lot of this will be crowd-sourced and grass roots. The legacy organizations got us into the mess, unlikely they can get us out (or even want to).

  10. JoeBrunner | | #20

    I was researching LG Therma V refrigerant to hot water systems and landed on this topic.

    A quick back story: Our home already has a good gas combi boiler hydronic heat system. I am looking into supplementing it with a heat pump to water system (ideally I'd be able to use the same condenser for cooling in the summer), but choices in the US seem to be very limited. I was looking at Dana Dorsett's reply above and he mentions LG Multi-V and HydroKit. However, I can't seem to find them on the US market. All I see is the LG Multi F LGRED (LMU480HHV) and can't find the HydroKit at all. Can you please help cut through all of the marketing talk and get to the core of these products?

    1. DC_Contrarian_ | | #21

      I looked into the LG HydroKit about two years ago. At that time there was limited availability, LG was only selling them to installers who had completed factory training. For the HydroKit the outdoor unit has to be from LG commercial range.

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