Tight house or oversized furnace?

[Comfy in MN]

Last night while watching TV I decided to time my furnace run times because I'm in the market for a new furnace that I'm thinking about going down in size.
Results: cycle 1, 5 min 10 sec furnace on 34 min 12 sec off
Cycle 2, 5 min 52 seconds on 33 min 35 sec off
It's fairly cold here now, 5 degrees F at the time I was doing the timing.

Equipment: 92.5% 67k btu furnace, Broan-Nutone HEPA HRV, t stat is set to 70 and it turns heat on at 69 and back off at 70

Im in the market for a new furnace and I'm thinking about going to a 45k but contractors seem hesitant to go that low for my home, but based on my unscientific test on run times I think I'll be just fine! What do you think? Is my furnace too big or is my house just well insulated? Thanks for your input!

[crmont]

Correct me if I'm wrong but doesn't it get much colder than 5 deg up there? And what was the wind like? The wind will make a big difference.

[Comfy in MN]

It does get much colder than 5*, -15 to -20 on rare occasions, but with such short run times it seems there's some room to work with, also wind was light around 5 mph.

[Comfy in MN]

I want a furnace that actually runs to keep a slow trickle of heat from the vents. When on for such a short time it isn't that comfortable.

[motoguy128]

Go down a size...or look at a combi boiler with outdoor reset control for even more even heating when paired with a hydronic air handler. You can also add a heat pump and gondfual fuel and have even lower output in mild wearher. You not far from design temp but only using less than 20% capacity. You should habe no trtoublke with a 45k unit. You probably only need maybe 30k or less even at-10f.

It not suprising. I only need 65k in a 3500sqft house with moderate insulation and lots of windows at 0f.

You have a very well insulasted home.


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[motoguy128]

Btw... great to hear a home owner that gets it...the benfit of smaller being better and more comfortable.

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[energy_rater_La]

x2

[Kevin Weaver]

I would consider a modulating furnace. The Lennox is really nice. This furnace can fire from 35% of its capacity to 100% in 1% increments. I would but in the 70,000 btu. and let it do its thing. Also its 98% eff.

[energy_rater_La]

rather than guessing about how tight the house/duct system is...
have a blower door & duct test done.

otherwise it is just a wag.

best of luck.

[beenthere]

Might want to look into a York mod. From 35% to 100%, in .5% increases, and comes in a 60,000 BTU size, so you aren't getting a furnace larger then you already have.

[54regcab]

The fact that your house has an HRV tells me the builder/insulator probably made an effort to make the house tight. 45K is more than plenty for a tight house. You have a 67k now because the HVAC contractor that installed it was scared to trust the insulation effectiveness.

[tedkidd]

X3 moto.

So you want a furnace that works like a faucet not a firehose, you want range. I think BT might have nailed it, that furnace may drop the lowest. 20k I think?

[beenthere]

21,000 input.