How important outside combustion air?
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  1. #1
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125

    How important outside combustion air?

    Hi,
    I've been so happy with the 2 stage/variable speed trane furnace for the main living area, i'm considering replacing the 17 y.o. single stage furnace xe90 upstairs (when I replace the failing air conditioner up there).

    The furnace is shoved in a closet, and sucks air from a ceiling louvered grill that connects directly to the attic. Dust particle collect along the cracks of the closet door, so i'm pretty sure a good bit of conditioned air is used for combustion.

    How important would adding a roof connecting PVC pipe to this set-up for intake air? Can I ask the pros and cons (my big con would be drilling the hole in the roof and getting it properly sealed)?

    Thanks

    Steve

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,273
    Does your house have a gable roof? If so the intake could be located in the gable end vs. through the roof.
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  3. #3
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,829
    We always install our high efficiency boilers and furnaces with outside combustion air/sealed combustion piping. A hole in the roof with proper sealing is not rocket science. You can easily hire a roofing company to put the flange in place if so desired. And to answer your question directly, combustion air is as important to your furnace as air is to you. Both need to breathe to survive.
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  4. #4
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    You asked:

    How important outside combustion air?
    Life or death is the answer! Would you like to continue to wake up in the morning?
    Using a giant opening to the attic certainly allowed enough combustion air to enter.....Probably way too much! to the detriment of your heating ( and cooling cost) You new unit should address this wasteful detail and still be safe. Probably a 90 percenter would answer your needs along with a good job of sealing/ insulating from a good weatherization/ insulating contractor
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  5. #5
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Quote Originally Posted by central nj View Post
    Hi,
    I've been so happy with the 2 stage/variable speed trane furnace for the main living area, i'm considering replacing the 17 y.o. single stage furnace xe90 upstairs (when I replace the failing air conditioner up there).

    The furnace is shoved in a closet, and sucks air from a ceiling louvered grill that connects directly to the attic. Dust particle collect along the cracks of the closet door, so i'm pretty sure a good bit of conditioned air is used for combustion.

    How important would adding a roof connecting PVC pipe to this set-up for intake air? Can I ask the pros and cons (my big con would be drilling the hole in the roof and getting it properly sealed)?

    Thanks

    Steve
    You pretty much covered the pros and cons... you don't want to compete with the furnace for oxygen and it will be a lot safer to have an outside source for combustion air. If the furnace is close to an outside wall, you can drill sideways instead.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

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