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Community and Q&A

Using Mini-split to supplement oil boiler for heat

Joefolker | Posted in Energy Efficiency and Durability on

We have a seasonal residence in Maine when we leave for the winter months (Oct – May).  We have a mini-split heat pump that we use June – Sept for heat and a/c needs.  My question is, does it make sense to keep our mini-split on through the fall, winter and spring season to supplement our oil boiler heating system?  I’m thinking that I’d run the mini-split at around 50F and the house heating system set for about 47F.  When it became too cold for the mini-split to keep up, the boiler would kick on and take over the need for additional heat.  Anyone have any thoughts on this?  Thanks in advance!

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  1. paul_wiedefeld | | #1

    At 50 degrees that minisplit will be extremely efficient. Probably 50%+ cheaper to operate than oil and could cover the vast majority of your heating needs (depending on size).

    1. Joefolker | | #3

      Thank you

  2. monkeyman9 | | #2

    I tend to phase on my pellet stove and oil heat once we get into the 20s outside. It keeps up pretty well until we get down to 20 or so and the reverse cycling is kicking in more and more. Then it's not as comfortable and the pellet stove goes on. We keep our house at around 68f all winter.

    At 40s and 50s outside the mini split is doing great still.

    The bonus room above our garage we use the mini split all winter no matter the temp. Room isn't quite as comfy but it works. I've been setting the temp in there to 65 and the oil at 60 (never kicks on). My Mitsubishi 15k just leaked on the side of the coil inside the house. I replaced it with a Fujitsu 12k that's sized better to the room. We'll see how that does.

    1. Joefolker | | #4

      Thank you!

  3. STEPHEN SHEEHY | | #5

    My only source of heat here in Maine are two minisplts. Right now, at current electric and oil prices, you get about twice as much heat output per dollar over the course of a winter from a minisplit. That's assuming a COP of 3 and a 95% efficient boiler or furnace.
    In most of Maine, your oil heat will never come on because the minisplit will still produce heat well below 0°F.

    1. monkeyman9 | | #6

      Had a -15f night at my house and ours were still going. Our bonus room with mini split only got to around 60 that night. Scared me a bit cause my boiler never kicked in in the main house with split and pellet stove going there since the pipes were in the outside wall.

    2. Joefolker | | #7

      Thank you!

    3. Joefolker | | #8

      Thanks Stephen! We leave the house vacant for the winter months. My concern was that if I left the mini-split running, and the temperature dropped too low outside, the mini-split would dump cold air back in the house forcing my boiler to run even more than not using a mini-split at all. But it sounds like, based on your experience, that wouldn't be the case.

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