Which minisplit to get?
I’m new to this site and have been reading a lot of info on minisplits. Could anyone tell me which size Mitsubishi FHxxNA series or Fujitsu model I should get for my house: a 24,000 sf split-level home in Zone 7. The cold weather gets to -30F or so in Dec. and Jan., so it would need to be the better heat-efficient one.
I have a Pacific Energy wood stove; here is the TECHNICAL INFORMATION for the wood stove:
Heat Output Cord Wood (BTU): 72,000 BTU
Heat Output EPA (BTU): 36,600 BTU
Emissions: 3.4 gm/hr
Firebox Size: 2.1 cu.ft.
Log Size (recommended): 18 in.
Log Size (max.): 18 in.
Burn Time (max.): 8 hrs.
In the -30F temps, it works, but burns a lot of wood per hour.
So with that said, could anyone help me on choosing the right minisplit unit for my application?
Just don’t want to get it too small or too big. I would just use the wood stove when it would be extremely cold.
Thanks for your help in advance.
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Are you sure your house measures 24,000 square feet? If it does, that's a pretty big mansion. Perhaps you meant 2,400 square feet?
Regardless of whether your house measures 2,400 or 24,000 square feet, it is unlikely that a single ductless minisplit unit will heat your house. Moreover, a ductless minisplit won't work when the outdoor temperature drops below about -10F or -15F.
The first step in designing any heating system is to perform a heating load calculation. You can hire an energy consultant (for example, a HERS rater or a mechanical engineer) to perform one for you. For more information on this topic, see these three articles:
Saving Energy With Manual J and Manual D
How to Perform a Heat-Loss Calculation — Part 1
How to Perform a Heat-Loss Calculation — Part 2
The largest single head versions of those series( MSZ-FH15NA or AOU-15RLS2-H) both put out about 15,000 BTU/hr at -15F and it's doubtful that just one of them would come close to heating your house fully at -30F temps, but if your ~36,600 BTU/hr stove is actually keeping up with the load, it's likely that a pair of them would, and one might be good enough to cover your average (but not peak) heat load.
The published HSPF effciency of the Mitsubishi is significantly higher than the Fujitsu at 12.0 compared to 10.3 (that's 16.5% more heat delivered per kwh with the -FH15 than the -15RLS2H).