Air source HP design question
Hi, I live in a 4a climate zone and require about 18 kW of heating based on Manual J assessment and a -20 C design temperature. It's a 3 story log house and all three floors will have radiant subfloor heat. I'll have two small fan boxes as well. I'm conflicted between two options. I'm looking at air to water heat pumps.
Purchase two separate 15 kW units that will each provide 9 kW at -20 C. The form factor of these is nicer for my desired installation location as they are relatively long and short. So this fits my design requirements very nicely.
Purchase a single 22 kW unit which is taller and won't fit in my ideal location and provides 13 kW of capacity at -20 C.
In scenario 2 I'll be utilizing our backup heat more often. This will be provided though resistive heating and wood burning stoves. However, the COP
I am somewhat drawn to Scenario 1 because it offers some redundancy in case one of the units fails (I'm purchasing from Ali Express). Although I would have each connected to different zones. However, scenario 2 will be somewhat easier to install.
Is dual air source heat pumps common? I see it with mini splits all the time of course but not very often with air to water. TIA.