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  1. #1
    Join Date
    Oct 2019
    Posts
    1
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    Re-Use Existing B-Vent For New Gas Insert?

    I have an old, manufactured wood-burning fireplace installed in a chase with a vertical vent. I believe that the existing vent pipe is B vent. I'd like to remove the old fireplace install a new "natural vent" (i.e. B-vent) gas fireplace. I'm not interested in direct vent as I don't want to see the flames behind glass.

    The question is, if the existing vent is indeed B-vent, I'd like to leave it in place inside the chase and just re-connect the new natural vent gas insert into the existing vent. I don't want to remove/replace the existing vent inside the chase if not necessary. Is this allowed and if so how do I reconnect the new insert to the existing vent - would a short section of flex duct work or would I need a special adapter.

    Thanks

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    25,722
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    Fireplaces have very strict venting requirements. Please follow them!

  3. #3
    Join Date
    Apr 2011
    Location
    SE Washington
    Posts
    634
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    venting must be sized and appropriate for each individual appliance, follow manufacturers instructions or buyer beware, and buy a good co detector...

  4. #4
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    7,273
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    B-vent is rated for 550F CAT I gas ONLY. It has an aluminum inner liner. Older factory built fireplaces use a stainless steel factory chimney listed for use only with wood burning fireplaces and are rated 1,700F max. The smallest are typically 8" ID. This chimney system is listed ONLY for use with that specific model fireplace. It incorporates either an air space cooling system or a non-ventilated insulation blanket or solid packed concentric space. The termination is the most important part of the system. Now, you may be able to burn vented gas logs in most of these fireplaces but not all.
    What you can do is run B-vent up the inside of this chimney and extend it above the top of the chase. However, by the time you remove the fireplace, you'll destroy the bottom of the chimney and it is not supported at the top so:
    Why kill yourself over trying to save a couple of bucks over a bastardized experiment. Do it right or not at all. Remove the entire fireplace and chimney and replace it with a very inefficient B-vented wasteful gas fireplace. Note that the whole world is going to direct vent as you're headed back to the stone age. If your house is weatherized to any degree a B-vent fireplace will very likely backdraft when its not wasting energy up the stack. Also, very, very few chases were ever properly weatherized.

    If you proceed with cobbling a gas fireplace vented with some bastardized connection to the existing factory chimney and there is a problem such as fire or CO exposure, you could be found criminally negligent. Why put yourself, your family or visitors to this hazard?

    This is NOT a DIY project. Do yourself a favor and hire a pro. What you are asking is a dangerous plan.

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  6. #5
    Join Date
    May 2004
    Posts
    13,637
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