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Will a Mitsubishi heat pump system be efficient for winter heating?

albertgabbay | Posted in Energy Efficiency and Durability on

I have a second home in East Otis, MA 01029, and plan to install a heat pump system. The home is vacant during the winter and the heat is kept at 50 degrees and have an oil hot water system for heat.

Will the heat pump system be effective in heating the main part of the house as it will be effective in cooling during the summer months? Thank you.

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  1. wjrobinson | | #1

    You are signing an installation contract with (your expert installer) and this person is the one to include in his contract the answer to your question. Not some unknown persons on the internet..... no?


  2. GBA Editor
    Martin Holladay | | #2

    In your climate zone, you can use either an oil-fired hydronic heating system (with an oil-fired boiler) or a ductless minisplit system to heat your house. Either system can work; it's up to you which system to choose. Unless your electricity prices are extremely high, the ductless minisplit system will cost less to operate than an oil-fired system.

    The biggest challenge with a system that uses ductless miniplits is heat distribution. This approach makes the most sense in a compact two-story house with an open floor plan. If you have a single-story house that isn't very compact, the approach is more challenging.

    Of course, you can always install several minisplit units -- for example, one in the living room, one in a hallway, and one or more in the bedrooms. This assures that everyone will be comfortable, but it raises the cost of the ductless minisplit installation.

  3. Expert Member
    Dana Dorsett | | #3

    Is this a ducted Mitsubishi, or a ductless? If ductless, is it in the Hyper Heating series, designed to handle low temp operation without icing up or breaking down?

    How much oil do you normally use over the winter, and which model Mitsubishi?

    IIRC the lowest setpoint setting for a Mitsubishi mini-split is 60F, not 50F, but even so even if you kept it at 60F the savings at WEMCO residential-retail electric rates (~16 cents/kwh ?) would be pretty good compared to 50F using $4/gallon oil in an 85% burner.

    With a 60F interior setpoint a Hyper Heating mini-split would run an average coefficient of performance of about 2.8 or maybe as high as 3.0 in that location. In rough terms, assuming it's 3, you get about 10,000BTU per kwh, and at 16 cents/kwh that's costing you abotu $16/MMBTU.

    A $4 gallon of oil in an 85% burner delivers about 117,000 BTU/gallon, or about $34/MMBTU, and there is also electric pumping & standby power to account for (but we since we can't, we won't.)

    So even if you're keeping it 10F warmer with the mini-split, the heating costs will be quite a bit lower.

    If the mini-splits are undersized for the heat load when it's 0F or colder outside, leaving the oil-burner active and set for 50F would be more than sufficient freeze protection.

    If it's your goal to get rid of the oil burner you may need to provide some resistance heat backup, with the thermostats set to a similarly low temp. As long as the mini-split is sized big enough to carry the whole load with a 60F interior temp at 25F outdoors (the mean temp in January in East Otis, according to data) the amount of resistance-heating power use won't be egregious, and it'll still come in well under the cost of heating it with oil.

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