Use existing duct system to allow a ductless minisplit to heat more rooms?
My parents live in Vermont, climate zone 6. The house was built in 2011 and is pretty high performing (ACH50 under 2, etc). They are interested in reducing or eliminating the use of gas in their home; right now it is only used for space heating. They have a forced air gas furnace. There are no great heat pump products today that would be a drop-in replacement for the furnace. Manual J heat load at the design temp of right around zero F is approximately 24 kBTU/hr, although based on their consumption and HDD, with aggressive setbacks they would see gas heat demand closer to 18 kBTU/hr at that temperature.
Options include: 1) wait for better ducted HP options to become available and 2) switch to ductless. I am here to ask about option 2.
The main living space (about 40% of the one-floor home) is quite open and would accommodate a ductless head pretty well, but the three bedrooms and 2 bathrooms would not get great distribution of the heat.
If if they put a ductless head (say a 1.5 ton unit) in the main room, could they run the air handler for the furnace to mix the air in the house and get heat to the rest of the rooms? Using small fans (eg bath fans or HRVs) for this purpose has been debunked on this site, but a full on air handler that is intended to serve a furnace/AC seems like it could work to link the temperatures in the bedrooms with the main space, and thus to allow a ductless head to heat the home. What do you think? Thanks in advance.
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