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Thread: Back drafting

  1. #1
    Join Date
    Feb 2010
    Location
    Omaha
    Posts
    143

    Default Back drafting

    I am not a home inspector and do not have a CO meter. I was at a customers house and noticed that at the top of the door to the basement that it was dirty as if air was being pulled through the gap. When the blower was turned on the door would be sucked closed.

    The top of the water heater had a rust colored coating but it did not appear rusted. In the basement I found 2 sections of return duct panning that were missing thus the return was being pulled from the basement. In 5 of the 7 returns screens had been installed at the floor level opening. In the basement I pulled the panning and found that there was screening at the basement ceiling level for the 4 2nd floor returns. 3 of the 4 2nd floor returns had the screens at both the 2nd floor and basement level.

    This home has a heat pump and a gas furnace. This was a cold winter and the furnace would have ran much more than in previous years. Would a furnace with a fan assisted vent have prevented back drafting of the furnace? This is not a 90+ with the PVC piping.

    The owner said that the CO alarms have never gone off and no one has experienced flu like symptoms.

    All of the screens were removed and the duct panning was corrected. It did reduce the door being pulled closed but did not eliminate it. I went over the seriousness of the situation with the owner and he should have it tested by the HVAC tech but he was not concerned.

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    Last edited by Robert Hronek; 04-12-2010 at 12:00 PM.
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  2. #2
    Join Date
    Mar 2007
    Location
    Plano, Texas
    Posts
    4,170

    Default Re: Back drafting

    Would a furnace with a fan assisted vent have prevented back drafting of the furnace?
    NO, a fan assisted furnace is still considered a natural draft furnace that relies on the buoyancy of warmer are to rise in the vent to draft.
    It needs combustion and dilution air and the area where the furnace is should not be under negative pressure.

    You are right to be concerned.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  3. #3
    Bob Spermo's Avatar
    Bob Spermo Guest

    Default Re: Back drafting

    Robert,

    Jim is correct. In addition, it does appear that the area where the furnace and water heater is located is under or os subject to negative pressure which can create backdrafting and/or spillage. Just because the home owner's CO detector has not detected CO does not mean there isn't any! Most CO detectors bought in stores do not give an alarm until 70 ppm which is 35 ppm above recommended 8 hr levels.


  4. #4
    Join Date
    Feb 2010
    Location
    Omaha
    Posts
    143

    Default Re: Back drafting

    I did inform him of the CO not alarming and may not alarm if the CO flucuates above and below the threshold level. I think the reason for the backdraft is related to the return duct being open in the basement along the the screens limiting return air from the 1st and 2nd floor.

    The 2nd floor supply is in the attic. Leaks in the attic could also cause backdrafting. I have urged him to have the HVAC tech do a worst case scenario with all the vent fans and appliances running.


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