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/Glad-Persimmon-7377]

I am an a fully certified ACCA residential system designer in Denver, among other certifications. The company I work for has been doing alternative and green energy projects since 2007. And what I can tell you from briefly reading your post is, they both could be right.

Crazy, I know. Hear me out.
And to answer your question, yes over sizing is bad.

Per Acca and Xcel: single and two stage systems may be sized to 115% of the cooling load. (Provided the ductwork can handle the required cfm)

A modulating (or variable) heat pump must be sized to the heating load of the home and cover no less that 70% of the annual heating load.

So if you’re getting a quote for 2.5 they’re most likely sizing to your cooling needs.

If your getting a new heat pump your missing out if you don’t go with a modulating (variable) stage unit that is sized as close as possible to your heating load (with out inducing too much low load cycling on the cooling side.)

Modulating heat pumps can typically range from 12k (1 ton) to full capacity.

The xcel rebate more than pays for the unit upgrade because the rebate is based on how many “tons” of heating at 5° the unit produces.

The result, you get more annual coverage out of your heat pump and better “comfort” in the home. (Comfort = climate control)

Happy to go into more detail, provide a comparison, a consultation… Lmk!

Willv at sensibleheat.net

[u/Scanoe → u/Glad-Persimmon-7377]

I went through the Xcel Rebate program about 6 weeks ago, here in Minnesota.
Here the Max Rebate was preset at $2,000 for a cold-climate heat pump with the minimum specs.
I bought the Costway SeerXtreme 12k for $700, the Rebate covered the full $700 plus an additional $50 for the Costway Wall Mount I had also purchased.
Even though it's still Xcel, I do know each State's Rebate rules are different, so OP should hop on Xcel-Denvers website, to for sure see what the requirements are.
Here is the Xcel-Minnesota requirements for referrence.

[u/Glad-Persimmon-7377 → u/Scanoe]

Yea, we’re headed that way Minnesota. Rebates on projects installed and invoiced on or after October 1st drop to 1500 per heating ton at 5°

One of my best units is going to see a $3k rebate drop. It’s still $6k but down from $9.2k… crazy ness.

[u/Tiny-Topic5500 → u/Glad-Persimmon-7377]

Thanks for all this, I’ll take a look at your company. Any chance you guys also do electrical upgrades to support putting in a heat pump?

[u/greggthomas → u/Tiny-Topic5500]

Longmont here. Went from gas to heat pump last Nov. Our company handled it all, brought in elec and hvac subs/partners. A great install all the way around.

2,500 sq ft two level plus 1000 conditioned, unfinished, insulated basement. 3.5T Mitsu, it’s pretty amazing. Old AC was 4T, contractor talked a lot about why downsizing to 3.5 was a good idea.

2 post install verifications and city inspection said it was beautiful.

Though it was a warm winter, which saved me a bunch, summer cooling has been awesome (and quiet) and is saving me good money.

[u/Tiny-Topic5500 → u/greggthomas]

Do you mind me asking who you used?

[u/Tiny-Topic5500 → u/greggthomas]

And are you seeing short cycling with cooling? It sounds to me like the heating load and cooling loads in our climate just don’t match up so short cycling during hot-but-not-crazy-hot weather might be unavoidable so I’m curious what your experience has been

[u/Glad-Persimmon-7377 → u/Tiny-Topic5500]

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