Geothermal quote after rebate coming back cheaper than air source
I am building a new house in CZ5/6 with a Manual J design temperature of -2F. The house is a ranch style with a walkout basement below. The footprint is 2500 sqft, so it is around 5k of total sqft. I requested a quote for 2 Mitsubishi SVZ+SUZ hyperheat ducted units, one for each floor, as having multiple units makes me more comfortable with air source units in case one of them dies in the winter (I see them as less reliable overall than the geothermal system, but maybe this is a bad assumption). I also got a quote for a single Waterfurnace 7 series with dampers to zone the main floor and basement. After the 30% rebate, the quote for geothermal is coming in a few thousand less. Quote includes drilling vertical loops beneath the home. Based on several sources, I really would like to choose this contractor, so I haven’t requested quotes from others.
A manual J hasn’t been run yet, but the quote is for a total of 5 tons. Based on the BetterBuiltNW HVAC sizing tool, I likely need more like 4 tons total, but I don’t think that will make a big difference in the situation here. I have an R15 slab, R21+R8 walls, .18 U windows, and R60 attic. Shooting for < 1.0ACH50, so I have already put money into the envelope.
I had originally decided to go with air source heat pumps based largely on raving reviews of the comfort of the system and it is great to electrify and expected the quote to be lower than the geothermal. Best I can tell from estimating energy usage, the cost to run the air source systems would be similar to a natural gas furnace. However, if I can install the geothermal system for similar or less money, then that seems best since it should use a lot less energy than the air source system in the winter.
Does anyone have any insight as to the comfort of the fully modulating Waterfurnace 7 with a 2 floor damper zoning system vs separate Mitsubishi ducted units? Seems like a large difference in comfort would be the only reason to go with air source given this situation.
Thank you for any input!
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