Fireplace and Furnace Flue Question

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by jer22, Feb 7, 2013.

  1. jer22

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    New Member

    Feb 7, 2013
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    Hi All,

    I'm a new homeowner that needs some clarification/assurance on a recent chimney inspection.

    I have an oil boiler in the basement and a traditional wood burning fireplace in the living room. The boiler is pretty much directly below the fireplace and vents through a separate flue to the left of the fireplace.

    When looking up the chimney from the fireplace, just above the damper, you can see the clay flue tile from the furnace flue. In other words, the furnace flue is exposed in the smoke box of the fireplace. With a bright flashlight shining on it, you can see about 18" of that flue tile before it disappears. Evident on the furnace flue tile is a 4" crack. I took the sweep's advice and had a stainless liner and cap installed for the furnace flue. So, I assume that side is good to go now. There's no way any exhaust is migrating out of the furnace into the fireplace side or into my living room.

    The question I have is about the fireplace side. Now that the furnace flue is closed off by virtue of the SS liner and cap, why would there be any problem with burning in the fireplace. I was told that it would be incredibly dangerous since you can't tell where the smoke will go. Is he asserting that smoke and creosote may still get into the old clay liner posing a risk?

    The house was built in 1962, and the previous owner was a retiree that had a fire going pretty much 24/7. The house is obviously still standing. Is this a case of what was once considered safe is no longer?

    Any help anyone can lend would be greatly appreciated!! Thanks!

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  2. webby3650

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    Master of Fire

    Sep 2, 2008
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    It likely wouldn't be a problem. There is a chance that smoke could be pulled through the crack in the flue that is servicing the furnace. If it's sealed around the liner at the top and bottom, then that wouldn't be a real risk. IMHO
    The flues are supposed to separated by 4"'s of masonry by code, this is called a wythe. So by code, you shouldn't use it.
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