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JECML | Posted in Energy Efficiency and Durability on

Do the low temperature air to water heat pumps work efficiently in mild climates? In western Oregon, my heating season starts October 15 ending April 1st, and nighttime lows average 30°F with 10 days or so in high teens, low 20’s. My design point is 18°F. I am interested in replacing my electric boiler with an AWHP, interfacing with an already installed 26 year old hydronic heating system.
Specifically, I am interested in the 60A ARCTIC HP and buffer tank. My AO Smith commercial 18KW electric boiler is 26 years old and approaching end of life, thus will need a new heat source soon.
Is it overkill to install the Arctic Heat Pump? I am not considering payback in the equation.

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  1. kyle_r | | #1

    What water temperature is your distribution system designed for?

  2. JECML | | #2

    12o°F. We have had temperatures as low as 13°. In those 2 incidents over the past 26 years, I had to turn up the temperature in the boiler to maintain the house at 68°. I also use the fireplace during very low temps.

  3. paul_wiedefeld | | #3

    Air to water would work, share how it goes! You could also plumb it so that you keep the existing boiler as backup.

  4. rhl_ | | #4

    Look at the SpacePak SIS-060A it’s the only split system on the market.

    My concern with monoblocs is if the antifreeze mix is off and the loop has no power, you’ve got a hard to fix mess on a cold day.

  5. Expert Member
    Akos | | #5

    Before looking at the equipment, I would run through this to see what you actual heat load is:

    You can convert monthly kWh usage to BTU by multiplying by 3412. With a 20F design, it will take a big or very leaky house to need 5 tons of heating.

    Lot of these air to water units show integration with domestic hot water. I'm not sure if this is ever really worth it. The cost of the indirect vs a standard buffer tank makes any ROI way too long, plus you still need a water heater for the final temperature lift. I would stick a standard resistance or HPWH and skip the indirect.

    1. JECML | | #6

      My house probably is leaky. The main living area 27 x 42 with 12’ walls mostly glass to the floor. The ceiling peaks at 19 ‘. We have two Hunter fans constantly circulating to bring the heat back down.The kitchen exhaust fan pulls 250 CFM when it’s on. The overall living space is 2800 sq ft. We keep the 3 bedrooms at 50° so it’s only the main living area that is set to 68°. It’s an architectural designed house with loads of R-30 insulation, however the Marvin windows have probably lost their insulating gas by now.
      The water temp into the floor is 120° and returns at 90°. The electric boiler pulls 74 amps. When the house was being designed, the electricity rate was 3 cents per KWH. Now it’s 13 cents.
      I might add that an 18kw boiler times 3412 equals 61415 BTUs (5 tons) The duty cycle of the boiler is about 75% so perhaps a 4 ton unit would also work.

      1. Deleted | | #7


      2. paul_wiedefeld | | #8

        Hmm a 30 degree delta T is a lot for a floor - is that when it first turns on or after it has run for a few hours? Floors are usually a 10 degree delta T, so you could use even lower temperature water.

      3. Expert Member
        Akos | | #10

        No need to guess, do the math in the article for an exact answer, well worth the time. The 75% duty cycle is a good start to ballparking it.

        Lot of the air to water heat pumps loose capacity bellow freezing, depending on where your heat load falls, a cold climate unit such as a SpacePak LAHP48 might be a better fit.

        If your place is at 4 tons and $.13 electricity, a heat pump upgrade of any kind will have a good ROI.

        Most houses have enough thermal capacity that a reasonable exhaust fan won't change the temperature. Plus you are also cooking at the same time, which adds back some heat, I wouldn't worry about it.

        Doing some air sealing would be well worth it as well. Besides reducing the amount of heat needed, it would let you run your heating loop colder which in most cases would buy you 10% to 15% increase in COP on an air to water heat pump.

  6. Deleted | | #9


  7. walta100 | | #11

    “I am not considering payback in the equation.”

    If this statement is true for, what reason would you consider an air to water heat pump?

    1 I have an extra 10k in my bank account and can’t think of a better way to get rid of it?

    2 My live is to boring with this simple electric boiler it almost never breaks I need the excitement that only a rare complex finicky machine will provide. Just thinking about how it could break on the coldest night of the year give me thrills.

    3 I want the “green” bragging rights of owning a unicorn system. It doesn’t not bother me that there are no spare parts or trained technicians within 200 miles of me. Remined me why am I not buying a ground source to water HP?

    I am sorry if any of my guesses are even a little close to the truth and hurt anyone feeling, but my mind just does not work that way. I can’t get out of bed without think about the return on my investment for doing so. I can’t think of a single good reason to buy a heat pump that is not about its lower operating costs.

    Help me understand your way of thinking what are the variables in your equation?


    1. paul_wiedefeld | | #12

      2/3rd fewer emissions and cooling are two additional reasons.

  8. JECML | | #13

    I’m not trying to invent the wheel here. The system is in and operating. I’m only interested in obtaining a more efficient way of heating water. As far as heat loads and etc are concerned, the contractor went through all of that with Wirsbo during construction 26 years ago.
    Since my boiler is at end of life, I reasoned the cost of a buffer tank is close to a wash.
    Now back to my original question. Has anyone had experience with the ARCTIC heat pump?
    And thank-you guys for mentioning Space-Pak. That’s a new contact.

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