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  1. #1
    Join Date
    Feb 2007
    Posts
    2

    Gas Furnace Venting problems

    Hi,

    We just had a home inspection prior to selling our house. We have a gas water heater & gas furnace tied together for the exhaust venting. The inspector noticed that there is noticeable backdraft into the gas water vent when the gas furnace is running. We took apart the metal vent ducts & no blockage was present. There is also a sizable ice build up on the chimney vent. What else could be the problem? The inspector assumed that something was blocking the vent but we found nothing on the inside. Could something be blocking at the cap? Due to the weather, we have not yet trekked onto the roof to check.

    http://home.comcast.net/~dkoffler/Untitled-1.jpg
    http://home.comcast.net/~dkoffler/Untitled-2.jpg
    http://home.comcast.net/~dkoffler/Untitled-3.jpg
    http://home.comcast.net/~dkoffler/Untitled-4.jpg

    Thanks

    Doug

  2. #2
    Join Date
    Oct 2006
    Posts
    41
    lets see a picture of the pipe where it comes out of the roof

  3. #3
    Join Date
    Feb 2004
    Posts
    2,597
    home inspectors generally do not know what they are talking about, he missed the foil tape on the water heater flue, it will burn/dry out after several years and fall off.

    To appease the new buyer, have a qualified hvac tech come check it out.

  4. #4
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,359
    looking at the top of the tank i would say you have venting issues somewhere in the mix.

  5. #5
    Join Date
    Aug 2002
    Location
    manitowoc wisconsin
    Posts
    4,943
    It is not uncommon to see induced draft furnaces spill out of a common vented water heater draft hood during prepurge.You should not have spillage after main burners light or if the water heater was calling for heat.All the elbows on the water heater flue & what appears to be single wall pipe on a 80 percent furnace do not meet national fuel gas code guidelines.call a heating contractor out to evaluate your flue & make the repairs needed.
    Take your time & do it right!

  6. #6
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    In our area the only way you can put an 80% furnace on with a water heater is to tie them together with 2 tees (not y branch) and a plug in the base. As far a single pipe, it depends on the btu of the furnace whether it needs to be B vent or not. If you have a lot of ice on the chimney then you have a problem, the draft cannot overcome all that cold air sitting in the chimney and spills out on the water heater, a much easier route for it to go.
    "Go big or Go Home"

  7. #7
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    You have had a serious problem there for some time judging by the looks of the water heater top.
    Flue gases have been spilling out that draft hood for some time for you & your family to inhale.

    The installation you have has the possibility to be a death trap due to the way it is installed.
    You are seeing the reasons first hand why an induced draft furnace common vented with a natural draft water heater can be dangerous due to the "designed" hole in the vent being inside the building envelope.

    There are ways to fix your installation & make it safe but you need to look for someone with the proper credentials.
    Most contractors will not know how to handle this scenario properly using guesswork instead of measurements to base their recommendations on.

    Check out www.nationalcomfortinstitute.com for contractors in your area that have been through Carbon Monoxide/Combustion analysis training.
    They should be able to help you find some solutions to your situation based on actual field measurements.

    Good Luck, this needs to be addressed ASAP.
    Have you set up a Google alert for Carbon Monoxide yet?
    Click here to find out how.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    What size is the furnace.
    How big is the room it and the water heater are in, cubic foot wise.
    What size is the chimney liner.

    You need a tech to address this.
    Contractor locator map

    How-to-apply-for-Professional

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

  9. #9
    Join Date
    Feb 2007
    Location
    Government base in the woods.
    Posts
    171
    Quote Originally Posted by markwolf View Post
    It is not uncommon to see induced draft furnaces spill out of a common vented water heater draft hood during prepurge.You should not have spillage after main burners light or if the water heater was calling for heat.All the elbows on the water heater flue & what appears to be single wall pipe on a 80 percent furnace do not meet national fuel gas code guidelines.call a heating contractor out to evaluate your flue & make the repairs needed.
    To add on to what mark said. Water heaters should have 3 inch flute vent, while your gas furnace should have 4 inch flute vent. I recommend running them seperately because if you have any problems it is easier to track down with seperate cap, collar and flashings for your furnance and water heart respectively.
    "Here in Carolina We Get-R-Done"

  10. #10
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,134
    Quote Originally Posted by davidr View Post
    You have had a serious problem there for some time judging by the looks of the water heater top.
    Flue gases have been spilling out that draft hood for some time for you & your family to inhale.

    The installation you have has the possibility to be a death trap due to the way it is installed.
    You are seeing the reasons first hand why an induced draft furnace common vented with a natural draft water heater can be dangerous due to the "designed" hole in the vent being inside the building envelope.

    There are ways to fix your installation & make it safe but you need to look for someone with the proper credentials.
    Most contractors will not know how to handle this scenario properly using guesswork instead of measurements to base their recommendations on.

    Check out www.nationalcomfortinstitute.com for contractors in your area that have been through Carbon Monoxide/Combustion analysis training.
    They should be able to help you find some solutions to your situation based on actual field measurements.

    Good Luck, this needs to be addressed ASAP.
    Follow the man's advise. I'm surprised your family hasn't had some serious health issues.
    Perhaps you should have read the instructions before calling.

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