Two ductless minisplit heat pumps for climate zone 6A
I’m trying to decide if I can utilize ductless mini split heat pumps as our primary source of heating. We will have a fireplace, but I can’t depend on this to supplement the required heat for various reasons. Budget is a factor, and what we are trying to achieve is something along the lines of the “pretty good house” idea. Not by any means a Passivhaus, but a stepping stone.
I posted a couple of months ago in regards to a pier foundation and insulating the floor assembly. Based on the constructive responses I received, I went back to the drawing board. I know some will argue, but based on the available materials, budget, available local contractors, this is the best I believe I can achieve for this project:
Wall (R-41.5):
-Hardie Lap Siding
-3/4″ plywood strapping
-2 layers 1.5″ foil faced polyiso taped seams
-2×6 stud 24″oc
-blown fiber glass
Attic (R-60)
Floor (R-42.5)
The house is 1895 sqft.
Is it possible to heat in our climate with two mini splits? Would multiple heads in the bedrooms help?
Thanks,
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Replies
Kyle,
Q. "Is it possible to heat in our climate with two minisplits?"
A. Yes.
Q. "Would multiple heads in the bedrooms help?"
A. Probably not.
There are lots of articles on the GBA site that discuss this issue. Use the "search" box and start reading.
Plenty of homeowners in Massachusetts and Vermont (where outdoor temperatures drop to -15 or -20 degrees F) are living happily in homes heated with one or two ductless minisplit units.
The first step you need to take is to do a heat loss and cooling load calculation. If you don't want to do the calculations yourself, you can hire an energy consultant to help you.
A compact house with few ells and bump-outs will be easier to heat and cool than a house that looks like a puzzle piece.
A house with few west-facing and east-facing windows will be easier to cool than a house with lots of west-facing glass.
If you want your plan to succeed, you'll need to leave your bedroom doors open during the day, and you'll need to accept the fact that your bedrooms will be a little cooler than the other rooms of your house on cold mornings (assuming you slept with the door closed). If your family can't accept these temperature variations, you may want to look at other ways of heating your house.