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Minisplits and steam

jlo1029jlo1029 Member Posts: 33
Hello great people of heating help.

I have a first world dilemma. I have both steam heat (gas) AND fancy new Mitsubishi hyper heat minisplits. I got the splits for AC but the hyper heat model was the same price due to state rebates so thus the upgrade. Boiler is 15 years old and probably not that efficient but works fine.

I live in New England. I suspect both systems can adequately heat the house and haven’t turned on the boiler yet this year. Does anyone have a good rule of thumb for when it makes sense economically to switch over?



  • SuperJSuperJ Member Posts: 579
    Dollar wise it’s probably a wash until the deep cold hits. But comfort wise the radiant wins. I would run it until the steam runtimes are long enough to justify cycling the thermal mass.

    I have one and for me I switch to natural gas and wood At night because the outdoor unit is bolted to the outside of a bedroom wall and the humming is annoying in the winter but not noticeable in the summer.
  • pecmsgpecmsg Member Posts: 1,450
    Hear's a calculator to come up with a rough #.

    Keep your comfort in mind, the heat pump WILL go into defrost from time to time. When you notice that its time to change over to Steam!

    10, 15, 20° every home and each occupant is different. Find your comfort zone!
  • mikeg2015mikeg2015 Member Posts: 1,178
    Run the mini splits until maybe 25-30f where defrost eats into efficiency and blowing air around feels drafty and not as nice as the steam heat.

    Then just use them for zone heating to fine tune temps in one area or room over another.
  • John Mills_5John Mills_5 Member Posts: 935
    Being Hyper Heats, probably have to hit 0 before they start to put out cooler air. Those suckers are amazing. Just experiment and see what you feel is best.
    jim s_2jlo1029
  • EdTheHeaterManEdTheHeaterMan Member Posts: 626
    SuperJ... do you know why the minisplit humming is bothering you in the winter and and not in the summer?
    It forgot the words to the winter songs

    but remembers the words to summertime songs!

    All good advise above, just remember that once you start using the steam (when it gets to lows of 20 F at night and 40 F high) stay with it ... don't be switching back and forth from HP to Steam and back to HP. there is a measurable increase amount of energy used to get the cold rads up to temp. Once the rads are hot the system cycles will use less gas to maintain.

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