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Number of Minisplit Heads for Small Home

hdreissigacker | Posted in General Questions on

Hi there!
A slight variation on the perennial mini split question. We are building a small (1000 sq ft) PGH in zone 6b. It is two-story, with kitchen/living upstairs, and bedrooms in a walk-out basement. My spreadsheet calculations are predicting  a heating load of about 8000 BTU/hr at -5 F, with the basement load being roughly half of the upstairs load. The levels will be connected with an open stairway. We had originally been assuming we’d use a single outdoor unit with two indoor heads, but all of the multi-split units are much larger than we need, in addition to being less efficient. I’ve read “Getting the Right Mini-split” quite a few times now and am still a bit flummoxed on the best solution for a very small house that has two heating zones: one unit? a very small/simple Fujitsu ducted system? I’ve read that “A compact two-story house can often be heated with a single ductless minisplit located on the first floor”…but when the bottom floor is bedrooms, which we would like to keep cooler, it seems less advisable to have the only indoor head be downstairs.  Any thoughts or ideas or experience greatly appreciated!

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  1. Kyle R | | #1

    I would describe your home as a single story home with a finished walkout basement. When you hear of accounts of people using one ductless unit on the first floor to heat the whole house , they are describing a home with both floors above grade. With an open stair well and a tight well insulated house this is doable because as you mentioned you can heat the downstairs and the natural rising of the warm air will heat the upstairs to within a few degrees. With upstairs bedroom this is ideal for most people. This works because the heat load of the first floor is at least that of the second floor, usually more.

    What you describe is the opposite situation. Your partially earth tempered basement will have significant less heat load than your first floor above grade. The basement will not call for enough heat to passively heat the main floor.

    If the floor plan upstairs is fairly open you could go with either a ductless or ducted mini split. If you don’t think you will have enough cooling load for the basement bedrooms to where you would need AC you could just go with electric baseboard there. Or you could put in a ductless or ducted mini split for the basement as well.

    What are your plans for hot water?

  2. hdreissigacker | | #2

    Thanks for your thoughts, Kyle. We will have a winter of full insulation but not living in the house, so we may experiment with one heat pump on the main floor and a fan or two blowing air downstairs and see how cold it is down there.

    We are leaning towards a resistance water heater, since we have a small mechanical room and don't really expect a cooling load in the finished basement.

  3. Kyle R | | #3

    It’s too bad the Sanden heat pump water heaters are so expensive. This would be a great application because you could use it to provide radiant heat to the basement as well as hot water.

    I don’t think blowing heat down stairs with a fan will make much of a difference. Blowing 70 F air into a 60 F area doesn’t transfer a lot of heat. You could use a plug in electric radiant heater in each bedroom I have seen mentioned on here.

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