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  1. #79
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    Anchorage Alaska / Seattle WA
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    Quote Originally Posted by Comfy in MN View Post
    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!
    According to my figuring based on averaging your two run times your house needs 42210 BTU's at 5 degrees. So 45K would be very very close if it gets much colder there.... but the idea of a modulating furnace is a very good idea...
    For the Government to Give Something to you - THEY HAVE TO TAKE IT WAY FROM SOMEONE ELSE FIRST...

  2. #80
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    Jul 2008
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    People design and operate based upon the way they define the problem.


    Are you heating houses up?

    Are you replacing heat lost?

    Are you managing cooling rate of occupants?


    Poor definition of the problem leads to poor solution design and poor/expensive operation strategies, like keeping settings too low and supplementing with resistance.
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  3. #81
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by genman View Post
    According to my figuring based on averaging your two run times your house needs 42210 BTU's at 5 degrees. So 45K would be very very close if it gets much colder there.... but the idea of a modulating furnace is a very good idea...
    I have a modulating furnace. On low, the air circulation is poor, the far end of the home does not get as warm as the close rooms. I live with because it is the master bedroom which ok. But expect poor circulation with adequate ducts and low firing rate. Heat prefers going up and cold goes down. At high air flow, closing dampers effects temp.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #82
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    Nov 2004
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    SW FL
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    smallest furnace available is all that needed or ...

    Quote Originally Posted by genman View Post
    According to my figuring based on averaging your two run times your house needs 42210 BTU's at 5 degrees. So 45K would be very very close if it gets much colder there.... but the idea of a modulating furnace is a very good idea...
    With run times only 20% of the OFF time on a 62,000 BTUH Output furnace,
    one would say that the heat loss is ~13,000 BTU/Hr at 5'F.

    Realistic?, that's a whole other story. [ i.e. house sits on top of a Hot Springs? ]

    I would believe ~28,000 BTU/HR at 5'F based on review of 2,100 sq foot residence with an EXCELLENT Thermal Building Envelope.

    MYSELF, I SURE WOULDN'T BE LOOKING FOR A DIFFERENT FURNACE.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #83
    Join Date
    Jul 2012
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    Thread Starter
    Dan, why wouldn't u replace the furnace with a properly sized one? I just timed a run at 28f odt, 70 t stat setting, results were, 6 min on, 25 off , so as far as my run time of last year at 5f, those numbers don't seem entirely accurate! All run times I've been sharing this year are 100% accurate! My house definitely doesn't sit on top of a hot spring, just well insulated I guess?

  6. #84
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    Jan 2004
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    Quote Originally Posted by Comfy in MN View Post
    Ok , just timed a cycle! -25*f, 10 mph w wind. 14 min on, 10 min off, stat set to 71.
    This post would indicate a heat loss of 39,083 BTUs.

    Quote Originally Posted by Comfy in MN View Post
    Dan, why wouldn't u replace the furnace with a properly sized one? I just timed a run at 28f odt, 70 t stat setting, results were, 6 min on, 25 off , so as far as my run time of last year at 5f, those numbers don't seem entirely accurate! All run times I've been sharing this year are 100% accurate! My house definitely doesn't sit on top of a hot spring, just well insulated I guess?
    This post would indicate a heat loss of 32,594 BTUs at -25ฐF. A 16% difference from the 2 timings.
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  7. #85
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    Thread Starter
    Would 1f on t stat make the difference or wind affect the discrepancy?? I promise that's what I've been getting!

  8. #86
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    1 degree does make a difference. About 1%, Wind is also a factor.

    Of course, if -25 with a 10 MPH wind is normal, then you would need to go by that loss, instead of a calm day at 28 degrees.
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  9. #87
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    Quote Originally Posted by Comfy in MN View Post
    Dan, why wouldn't u replace the furnace with a properly sized one?

    I just timed a run at 28f odt, 70 t stat setting, results were, 6 min on, 25 off ,
    so as far as my run time of last year at 5f, those numbers don't seem entirely accurate!

    All run times I've been sharing this year are 100% accurate!
    If your furnace maintains the rooms within 4 degrees of each other, IS there ANY Benefit to a New, Smaller furnace?

    I mean, other than, you are so Wealthy that the $$,$$$,$$$s in your wallet tend to Burn Holes in your Pocket.

    You may have the best THERMAL BUILDING ENVELOPE home in MN?!..!!...!!!
    Or U.S.?
    Or North America?

    TWO STORY ?

    2,100 Square Feet?

    What do you have for insulation?
    8 inches of foam on ALL SIDES.

    DO YOU HAVE < 10 WINDOWS?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  10. #88
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    Jul 2012
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    Thread Starter
    2100 sq ft split entry, 1050 up, 1050 down with walkout! I would show you a you tube video of my house when it was on the market before I bought it but I don't want my address in a public forum! All the rooms are within 2 degrees of each other!

  11. #89
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    Jul 2012
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    Thread Starter
    My plan is to have the current Armstrong furnace installed in my 3 car garage and install a 2 stage variable in the house! That's why I'm trying to educate myself on the furnace with the best overall comfort! Yeah the 67k I have now works great but it doesn't run long enough to get the comfortable feeling, my solution? Turn up the stat!!

  12. #90
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    Have you had a blower door test? Do you know the cfm50 #?

    Probably a 60mod will be your best option, pretty sure they ramp down the lowest, around 20,000 on low.
    Last edited by tedkidd; 01-12-2014 at 10:53 PM.
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  13. #91
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    Quote Originally Posted by Comfy in MN View Post
    My plan is to have the current Armstrong furnace installed in my 3 car garage and install a 2 stage variable in the house! That's why I'm trying to educate myself on the furnace with the best overall comfort! Yeah the 67k I have now works great but it doesn't run long enough to get the comfortable feeling, my solution? Turn up the stat!!
    What is the Relative Humidity in each area of the house?

    Run time should not affect Comfort level if the temperature varies by < 3 degrees from room to room.

    I don't believe Your Run Time is going to increase noticably unless the heat rate is < 15,000 BTU/HR.
    And that still will not solve the Comfort issue.
    _______ What is COMFORT? Well, IT AIN'T JUST TEMPERATURE ! _________
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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