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  1. #1
    Join Date
    Feb 2011
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    Default Smoke from fireplace in basement

    Recently, a mystery popped up which confounds the chimney sweeper I consulted. After the installation of a high-efficiency condensing gas boiler, suddenly some of the smoke from the fireplace in the living room ends up in the basement below. The previous boiler's exhaust gases went up a flue in the chimney, which also has the fireplace flue in it. We believe this boiler flue is fully closed off up top and below (new boiler has its own new PVC intake and exhaust pipes). Still, the basement becomes thick with smoke when using the fireplace in the living room above it. There is adequate chimney draw as the living room remains smoke-free when using the fireplace. Thanks a lot in advance for helping me with this most vexing problem.

  2. #2
    Join Date
    Aug 2007
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    Default Re: Smoke from fireplace in basement

    Sounds like the abandoned flue isn't totally closed off in the basement which is where the smoke is coming from.
    Now, there needs to be a reason for the smoke from the fireplace entering that abandoned flue in the first place. Either the problem is at the top of the chimney where the abandoned flue is supposedly closed off ---- or ---- there is a leak between the fireplace and the abandoned flues somewhere inside the chimney.

    That would be my guess.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
    Join Date
    Dec 2010
    Location
    Houston Texas
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    Default Re: Smoke from fireplace in basement

    I had the same thing happen to me.

    Your house is developing negative air pressure. When you use the house heater along with the fireplace, you are not getting enough air coming into the house to feed the fireplace and HVAC system. The open gaping hole is the flue to the HVAC system. The fireplace has greater air flow requirements and higher flue temps, so it winds up winning the air battle.

    To make an effective repair, you need to have a fresh air supply to the firebox and to the HVAC system. The size of the exhaust flue for the chimney should be the size of the fresh air supply for the chimney, at least 6" diameter. Capping off the fireplace intake pipe when nit in use is common.

  4. #4
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    Default Re: Smoke from fireplace in basement

    Quote Originally Posted by HoustonRemodeler View Post
    I had the same thing happen to me.

    Your house is developing negative air pressure. When you use the house heater along with the fireplace, you are not getting enough air coming into the house to feed the fireplace and HVAC system. The open gaping hole is the flue to the HVAC system. The fireplace has greater air flow requirements and higher flue temps, so it winds up winning the air battle.

    To make an effective repair, you need to have a fresh air supply to the firebox and to the HVAC system. The size of the exhaust flue for the chimney should be the size of the fresh air supply for the chimney, at least 6" diameter. Capping off the fireplace intake pipe when nit in use is common.
    The op posted his boiler is a direct vent with one for the combustion intake which doesn't draw air from inside ---- so I doubt that's the case.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
    Join Date
    Dec 2010
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    Houston Texas
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    2,969

    Default Re: Smoke from fireplace in basement

    It may still be the case if he is developing negative air pressure. The fireplace could very well be using the intake pipe of the HVAC system to get the air it needs for combustion.


    The HO can conduct a test by running both the fireplace and the HVAC. Sniff at the intake pipe of the HVAC. Get a feel for the volume of air flow at the HVAC when the fireplace is running. Compare that to the air flow when just the HVAC is running. The smell is coming into the house, mostlikely through the intake of the HVAC system.

  6. #6
    Join Date
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    Default Re: Smoke from fireplace in basement

    If the air intake is direct vented to the outdoors and is part of the sealed combustion chamber of the boiler then how would negative pressure occur ?

    Also , the op mentioned there is no smoke issue at or around the fireplace itself --- which is where you would most likely expect it from an issue of negative pressure or back drafting.
    Last edited by canuk; 02-27-2011 at 10:20 PM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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