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I am in the middle of a deep energy retrofit of my house, and a quick-and-dirty online manual J calculation of the projected loads once my projects are completed shows an estimated heating and cooling load of only 13,000 BTUs, compared to the current baseline of 41,000 heating / 28,000 BTUs cooling.

Since this is such a small number, my existing 125,000 BTU furnace will become even more ludicrously oversized than it is now. So I'm considering replacing it with a single ductless mini-split heat pump.

Here's my quandry: the numbers alone say that a single-headed heat pump unit should easily be able to handle both the projected heating and cooling loads. But I'm worried about getting the conditioned air consistently into the three bedrooms, which in typical ranch house fashion, are on the other side of the house from the living area, accessed through a hallway. The living area will probably be fine, but I'm worried that the bedrooms might not get enough of the conditioned air, even with a sealed and well-insulated building envelope (R-26 walls, R-50 ceiling, R-20 footing insulation).

If a single unit will be enough, where should I put the unit? In the living area above the entrance to the hallway? If a single unit won't be enough, would a double-headed unit with a single outside compressor work? Where should I put the other unit?

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