Q&A Using Existing Chimney for two gas appliances

QandA Posted By QandA, May 23, 2002 at 2:20 PM

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  1. QandA

    New Member 2.
    Staff Member

    Nov 27, 2012

    I have an older home that has block chimney with a 8x8 flue that runs up through the center of the house. The chimney is already being used by a gas-fired boiler and hot water tank. I want to put in a b-vent gas fireplace and run a 4" liner down the chimney, but i'm not sure if I can do this or how I would cap the chimney.The local dealers are not any help at all. Thank You


    NO. The code does not allow for common venting around the perimeter of a vent liner. You could run 2 liners, a 4" liner for your fireplace and another appropriately sized liner for the other two appliances.

    What you might want to look into is venting all three appliances into one larger common liner. To do this you'd need to confirm that all three units are category I (one) vented appliances. A category I appliance is identified as follows: "Equipment which operates with a non-positive vent pressure and with a vent gas temperature of at least 140 F above it's dew point". For example, a B-vent fireplace is category I. The rating plate on your gas-fired boiler and hot water tank will identify the category of venting.

    If there's not a second story above the fireplace, I'd simply vent it straight up with new B-vent. That would be the least expensive method.

    It all gets a little complicated for the average guy, but doable if you are willing to take the time to learn. Here's some links that speak specifically about Category I venting and venting tables for B-vent.



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