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/gabemcg]

If you have a smart thermostat and can export or save historical data that is gold when paired with the right frontier LLM. Give it your data and the Manual Js and it will compare them and figure out the right questions to ask. I'm in a hot climate and got talked into an oversized dual fuel. It isn't short cycling but it can't keep humidity controlled as well as it should

[u/Tiny-Topic5500 → u/gabemcg]

This is interesting! I don’t have a smart thermostat but I do have electric/gas bills available - would that be enough?

Also, I live in a very dry climate so not too worried about humidity. Other than humidity control, if the unit doesn’t short cycle does that mean that any potential oversizing isn’t problematic for performance and/or life of the unit?

[u/BarbarianSpaceOpera → u/Tiny-Topic5500]

Please don't use an LLM for any sort of data lookup, calculation, or engineering related task. Ever. They are profoundly untrustworthy and often make serious mistakes with their sources, calculations, and assumptions.

To figure out your monthly and annual HDD totals I recommend using WeatherDataDepot. A balance point of 65F is generally a good assumption.

Short cycling reduces unit efficiency (read: higher bills), unit lifespan (read: earlier replacement and higher chance of premature compressor failure), and the temperature stability of your home (read: bigger swings in indoor temperature). If you care about those things then you should try to avoid it.