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  1. #1
    Join Date
    Mar 2013
    Posts
    6

    Outside air sailing in and around fireplace

    I have a ~1980 Fireplace Manufacturers Inc. Model 42A fireplace insert. Fireplace Manufacturers Inc of Santa Ana sold the company to DESA International in 1998, which filed for bankruptcy in 2008. They maintain a website, desatech.com, but it does not have the model 42A listed. It is a metal insert, with firebrick lining.

    The flue is a round cylinder connected with the firebox. The chimney is a wood and stucco frame, covered by a 2x4 metal cap. The house is in Los Angeles.

    Above the mantel there is a hole in the drywall for TV cabling. Through that hole I can feel a literal breeze, so the chimney housing must be open to the outside somehow. I did not pull away all the insulation from behind the wall, but it appears that the "chimney" does not have a wall that separates my drywall from the chimney, as my drywall above the mantel apparently forms the fourth wall of the chimney, the other three walls are on the house exterior.

    Also, on opposite sides of the firebox, facing towards each other from the side (just inside the metal firebox itself), are what look like vents. I get a lot of cold air in through those as well.

    I took a can of foam into the attic and sealed up any openings that I could find between the attic and the stucco chimney, but the chimney is a structure on the outside of the house, so it was not really open into the attic anyway. The sealing had no effect on the breeze through the drywall.

    My questions are: (a) whether these drafts can be caused by a flue that is not sealed to the metal cap at the top of the chimney, (b) can I put a tight seal around the flue and metal chimney cap to stop this draft, and (c) will sealing the flue to the top cap have any effect on the draft on the vents inside the fireplace?

  2. #2
    Join Date
    Dec 2011
    Location
    PA
    Posts
    199
    It could be poor sealing around flue. Most likely it is poor construction of the chase/chimney. A fireplace is not designed to completely seal the hole they sit in. They actually have holes cut into them to allow air to flow in and around the fireplace cooling the metal so they can maintain close clearances. The structure of the chase is to be constructed like a exterior wall, which means the walls should be constructed using plywood covered with a tyvek or equivalent, sealed, and well insulated. Most air infiltration problems that I run into are because the builder didn't know what he was doing.

  3. #3
    Join Date
    Mar 2013
    Posts
    6
    Thanks. From what I've seen around the house, an incompetent builder seems likely.


    So it would be OK to seal the flue to the metal chimney cap? I was just concerned that it might need that air circulation.

  4. #4
    Join Date
    Dec 2011
    Location
    PA
    Posts
    199
    I'm not sure I understand what you're asking. does the flue pipe come up through a chase cover at the top of chimney, then they connect to a cap? Depending on how the chase is constructed and what termination they used at the top, I can't tell you one way or another. There are so many types of installations that without seeing the installation there is no way for me to be sure on whether you can seal it or not.

  5. #5
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,180
    search this forum for previous discussions about cold air infiltration.

  6. #6
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    [QUOTE=darthvader;15346511Most air infiltration problems that I run into are because the builder didn't know what he was doing.[/QUOTE]

    Or the subs, or the building inspector...
    If more government is the answer, then it's a really stupid question.

  7. #7
    Join Date
    Mar 2013
    Posts
    6
    Quote Originally Posted by darthvader View Post
    I'm not sure I understand what you're asking. does the flue pipe come up through a chase cover at the top of chimney, then they connect to a cap? Depending on how the chase is constructed and what termination they used at the top, I can't tell you one way or another. There are so many types of installations that without seeing the installation there is no way for me to be sure on whether you can seal it or not.
    When I say "metal chimney cap," I mean one of these

    http://www.google.com/url?sa=i&sourc...63319591657433

    Attached to that, there is a typical rain shield. I'm not sure if that helps.

    hearthman, I will do that search, thanks.

  8. #8
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,180
    What your link shows is a "chase top or flashing". The chimney pipe protrudes through this and attaches to either a round listed termination with a storm collar below it or a square type termination with a telescoping element that extends down into the last chimney section. Note that some mfrs. require the chase top you show to sit on metal spacers so air can flow into the chase. Can you post a pic of your actual chimney termination cap?

    BTW, what you call the "stucco chimney" is technically the "chase" and the metal pipe coming up out of it is the actual "chimney".
    HTH

  9. #9
    Join Date
    Mar 2013
    Posts
    6
    hearthman - thanks for the reply and the terminology. I don't have a pic of the actual chimney termination cap, as I don't have a tall enough ladder. I was hoping to see if there is a proper technique for the "fix" before I hired a contractor or bought myself an extension ladder to address this.

  10. #10
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,180
    Pete, to answer your questions about air sealing, no you can NOT seal the gap around the chimney where it penetrates the chase top. This is a calculated air infiltration/ exfiltration point to ensure adequate cooling air in and respiration of heated air out so temps. don't exceed design. There should be a firestop at the ceiling level and another at the attic, both of which can NOT be caulked, chinked or otherwise sealed for this purpose. Even with old triple walled thermosyphon chimney, the chase still needs cooing air for the fireplace itself not to run too hot.

    HTH,

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