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  1. #1
    Join Date
    Dec 2011
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    Rhode Island USA
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    Default Sealing glass doors on stone faced fireplace

    Hi guys,
    I've purchased a 42" wide glass bi-fold door unit for my fireplace. There is four bracket tabs to fasten this unit to the firebox masonry. The fireplace surround is natural stone and not brick and because of this a simple gasket isn't going to seal the door assembly to the fireplace surround. The stone is irregular and gaps between the glass door frame and fireplace are as much as 2 inches and as little as 1/8". I was considering using a standard masonry mortar, mixed rather stiff and apply this to fill the gaps between the doors and fireplace. The other option was using a masonry caulking product which I think would be easier to apply as a trowel will be difficult to get the mortar deep between the frame and the fireplace surround.
    My concerns are if I use a non flexible material (like mortar) will it crack? Will the heat alone crack the product? The door frame is steel which will contract and expand with the heat of the fireplace. I don't want to have to do this job twice so I'm asking the advice of others.
    Thanks,
    Chris

  2. #2
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,381

    Default Re: Sealing glass doors on stone faced fireplace

    I think you are going to have a hidden issue here, but I will discuss that later. For your question, you need to do both. Start with the mortar to reduce the gaps all around the glass door frame to about 1/4", then use the masonry caulk to finish sealing. The caulk wont effectively fill a 2" gap, and you are right to be concerned that the cement will not flex and end up cracking.

    The hidden issue here is supplying air for combustion. Most fireplaces use room air for combustion, which reduces oxygen content in the room and reduces the efficiency of the fireplace. If your doors provide a small amount of room air to slow down the burn of the fire, then OK, except that you will need to keep an eye on the chimney for creosote buildup.

    The other, and better option would be to bore a hole in the back of your fireplace to the outside and add a duct, about 1.5" in diameter to provide fresh air to the fire. You will need to cover the opening to the duct with some kind of screen to keep bugs and critters out. This way you will not use your heated and conditioned inside air for the fire. Any heat from the fireplace will stay inside the house.

  3. #3
    Join Date
    Dec 2011
    Location
    Rhode Island USA
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    2

    Default Re: Sealing glass doors on stone faced fireplace

    Hey Keith,
    Thanks for your quick reply. My issue is only the sealing of the doors as I have combustion air being supplied by ash dump door under the fire grate. There is a 9" X 4" cable controlled vent in the chimney cavity under the firebox on the outside of the chimney. The doors on the fireplace can be 100 percent sealed because of this system.

    A note on the vent being on the back of the firebox. I've did some testing with that design on a markup of this fireplace. Two MAJOR issues that I found by placing the combustion vent on the rear of the fire box.

    1) Because cold air is heavier than warm this vent will spill cold outside air (in the winter of course) into the firebox. Of course you could put a cap on it...but it has it's limitations to controlling air intake. Having the intake vent under the fire grate completely eliminates this issue. Because the air is cold it stays under the firebox (even when this intake door is kept open no cold air will come up into the firebox) until the fire is lit and of course then from the convection of the fire pulling for air (when the glass doors are closed) it pulls the cold air to feed the fire. The ash dump door is also controlled as a damper from a push/pull cable to control the air being supplied to the fire.

    2) Naturally the smaller the intake hole the faster the air will rush through it. Even with a large opening on the rear of the firebox the air rushing in will cause the flames and ash to be pushed towards the living space. Trust me on this...this isn't the ideal place for the intake vent.

    I'm installing a heat exchanger soon to finalize this project. Once that is done this fireplace will actually be a heat source rather than a heat extractor. Looking forward to that day.
    Thanks for you input Keith. I think your approach on sealing up those doors is good advice.
    Chris
    Last edited by eportel6607; 12-26-2011 at 01:59 PM.

  4. #4
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
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    Default Re: Sealing glass doors on stone faced fireplace

    Looks like you will have a good setup when you're done.

  5. #5
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Sealing glass doors on stone faced fireplace

    Quote Originally Posted by keith3267 View Post
    I think you are going to have a hidden issue here, but I will discuss that later. For your question, you need to do both. Start with the mortar to reduce the gaps all around the glass door frame to about 1/4", then use the masonry caulk to finish sealing. The caulk wont effectively fill a 2" gap, and you are right to be concerned that the cement will not flex and end up cracking.

    The hidden issue here is supplying air for combustion. Most fireplaces use room air for combustion, which reduces oxygen content in the room and reduces the efficiency of the fireplace. If your doors provide a small amount of room air to slow down the burn of the fire, then OK, except that you will need to keep an eye on the chimney for creosote buildup.

    The other, and better option would be to bore a hole in the back of your fireplace to the outside and add a duct, about 1.5" in diameter to provide fresh air to the fire. You will need to cover the opening to the duct with some kind of screen to keep bugs and critters out. This way you will not use your heated and conditioned inside air for the fire. Any heat from the fireplace will stay inside the house.
    As a note --- modifying your fireplace to include a fresh air intake isn't really a DIY project --- it's against most codes. It really should only be done by a fire place spec1allist and usually has to be permited and inspected.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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