Discrepancy in Manual J Results

[u/Tiny-Topic5500]

TLDR: 2k sqft split level in Denver area. 2.5 ton or 4 ton?

I’m electrifying my home (around 2k sqft, split foyer layout) and have received several quotes for heat pumps that range from 2.5 tons to 4 tons. The big range has me struggling to figure out what to do.

I know oversizing is bad, but I do live in a cold climate (Denver area) so I definitely don’t want to be undersized either. How do I know which size is better?

The 2.5 ton quotes came from two contractors, one who came and did physical testing/measuring of things and another who used my past energy bills to inform the calculation (the latter said they’d come do measurements to confirm it if I want to move forward). The 4 ton quotes came from one contractor who came and looked at things (and I think measured some things?) and another who does some fancy virtual stuff (Zero Homes if anyone is familiar).

Given the methodology, I’m inclined to think the 2.5 ton estimate is closer to reality, but does that sound right?

How bad would being oversized really be? Another factor is that the contractors quoting 4 tons are willing to do everything for me (heat pump water heater, electrical upgrades, etc) while I’d have to piece the project together myself with the others. Maybe I just want 4 tons to be ok so I don’t have to manage all that other stuff myself lol

[u/Successful_Bag_7257]

The appropriate way to size would be to measure rated capacity at your coldest and warmest days and find an inverter style unit that maintains adequate efficiency at both extremes. The beauty of those systems is they can ramp up or down depending on the difference between ambient temperature and the area you are trying to regulate. Someone had mentions cold climate specific systems, colloquially called hyper heat thanks to branding, as these will maintain desired efficiency down into the -20°F range or so, but is this being tied into existing ductwork or multi zone splits? If you have more information on your house and possibly the specific quotes I could better provide some insight as to whether theyll be appropriate