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  1. #1

    Tight house or oversized furnace?

    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!

  2. #2
    Join Date
    Oct 2005
    Location
    Pacific Northwest
    Posts
    2,267
    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.

  3. #3
    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.

  4. #4
    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.

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    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.


    Sent from my SGPT12 using Tapatalk 2

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Btw... great to hear a home owner that gets it...the benfit of smaller being better and more comfortable.

    Sent from my SGPT12 using Tapatalk 2

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,200
    x2
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #8
    Join Date
    Jun 2007
    Location
    Greenwood Indiana (Indianapolis)
    Posts
    420
    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.
    As iron sharpens iron so one man sharpens another Proverbs 27:17 NIV84

  9. #9
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,200
    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.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    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.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,311
    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.

  12. #12
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,736
    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?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    21,000 input.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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