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  1. #1
    Join Date
    Feb 2014
    Posts
    7

    Confused Two stage furnace sizing coldest days a problem, Help

    Original furnace was 75,000 btu input and 52,500 output, single stage, heat loss of home is 48,480 btu's. New furnace is 66,000 btu input and 52,800 output high fire. Second stage is 42,900 btu input and 34,320 output low fire. Should a two stage Furnace be closer in btu output in 2nd stage (34,320) where it is running most of the time to my original furnace (52,500) with a heat loss of 48,480. It seems to me that in low fire (34,320) it can not keep up with my homes heat loss of (48,480). Then high fire has to run much longer to catch up due to heat loss. I am now running all the time in high fire as settings were changed, and I am still having a problem moving my temperature up from 68 degrees sleep, to 72 wake. It takes 3 to four hours to get to 72 degrees. Original furnace did not have a problem with night time to wake settings.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    May not have been set up properly when installed. Call the installers back to check it and do a proper set up.
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  3. #3
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,963
    What beenthere said; it could be that the furnace is NOT delivering its Rated Btu/Hr to the conditioned space.

    Could have Return-Air leaks from a cold attic or garage area, etc., or leaky improperly insulated duct system.

    Everything should be checked for proper performance.

  4. #4
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    A BTU is a BTU. New or old, single, two stage or mod. The actual output needs to be verified. As far as actual sizing, I would expect under normal conditions the first stage would be more than adequate 75-85% of the time.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  5. #5
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,529
    One other thing to consider is what size drive the old furnace had compaired to new one.

    I have ran into that before and had to make adjustments with the system with speed taps. Ductwork could have alot to due with also.

    Just like everyone else has said have the installing company back out to check everything and do some testing to ensure the system is working properly.

  6. #6
    Join Date
    Oct 2006
    Location
    The Beach
    Posts
    701
    The design temperture for your area might need to be changed because of the cold weather we had this winter. Beenthere has some good advice.
    Blue Fox

  7. #7
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,529
    Quote Originally Posted by lentz View Post
    The design temperture for your area might need to be changed because of the cold weather we had this winter. Beenthere has some good advice.
    Agreed it will be interesting to see if the average temp for all areas will be changed after this year of extreme cold over the country. While I doubt it, I could be wrong.

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