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Community and Q&A

Drafty Gas Fireplace Insert

New2Alberta | Posted in General Questions on

In the winter (Alberta) we get huge drafts coming in the grills of our gas fireplace insert. I’ve noticed it when it’s not in use, especially at night but it seems inconsistent and not necessarily predictable by the temperature or audible wind. From the outside there is a fresh air intake on the chimney and there is a metal chimney exiting the top of the old stucco chimney.

What can I do here? Who would I even call to look at it? My husband likes the fireplace but I am really concerned about the draft coming in when it can be -30 C here and our winter is long.

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  1. davidmeiland | | #1

    We've been working on a house with a gas insert fireplace, and a LOT of air was coming in through the sheet metal housing when we had the blower door running. This is a direct vent unit with a single pipe out the top and through the roof. We went up in the attic and could see that the builder had framed a chase for the vent pipe, and had put a plywood ceiling above the unit, but had cut a very large hole for the pipe, and not installed a sheet metal draft stop. We were able to install one at the attic floor level by cutting a clean hole in a piece of sheet metal, cutting it in half, then installing it around the pipe. This is allowed by the manufacturer of this particular pipe system, in fact they make parts you can buy for this purpose if you want to. The other thing we did was to make sheet metal caps to cover a couple of large holes in the housing, in the space below the burner. These holes are punched by the manufacturer so that the plumber and electrician can run the gas and electrical connections without drilling the housing. We got a lot of improvement on this one but it is hard to make them perfect.

    As far as who does it... a sensible HVAC contractor, a building performance contractor, whoever is in your community that is fluent with this stuff. The average contractor probably is not.

  2. New2Alberta | | #2

    Ours is a retrofit into an existing fireplace chimney which I'm not even sure I can see from the attic. The original inside vent was filled in and sheet metal was used to fit in the remaining space around the insert. For some reason they set it up a few inches above the brick hearth so there is sheet metal on all four sides, not caulked at the inside edges and with a few screws holding it on. Not sure how I would get to the chimney at this point?

    I noticed on the outside of the house there is a little bit of stucco missing at the one bottom corner (it sits out like a cantilever) so I wondered if that was part of the problem.

  3. GBA Editor
    Martin Holladay | | #3

    The necessary steps are the same air-sealing steps required for any part of your thermal envelope. However, many builders neglect these steps behind metal fireplaces. Once the fireplace is installed, there is often no good way to solve the problem without removing the siding on the exterior side of the fireplace.

    Each installation is different, of course, so it is hard to assess how to proceed without a site visit. Here is an article with more information on air sealing fireplace niches:
    How to seal 4 common air leaks in your house.

  4. davidmeiland | | #4

    There must be home performance contractors, insulation/air-sealing companies, even clever HVAC people in Alberta--it's cold up there. Finding the right person is key. If they don't own a blower door that's a bad sign. If they do, they would set it up right away and start figuring out where the air is and where they can stop it. Martin is right, it can be hard, but if there's good news, yours sounds like a retrofit so it may be possible to modify the installation. Once they're installed in new construction it's hard to change anything.

  5. New2Alberta | | #5

    Unfortunately there is stucco on the outside of the chimney, not siding, so it can't be removed and replaced easily. I would think going through the outside would be pretty pricey since I would need to redo the stucco on the entire chimney. Is it a better option to have the fireplace removed and reinstalled properly (or replaced)? We tried blocking the grilles with magnets while it's not being used but I can't even do that effectively because the bottom is open under the control panel grille not just the front.

    Is the cold air coming in a risk for backdrafting at all? It can be a really large volume of cold air coming in, even when blocked by magnets and pillows.

    You would think houses in a climate that can be -30C would be well sealed (or at least well insulated), but not so. I live in a small town 1.5 hrs north of any major cities. So while I'm sure there are lots of really thorough insulation and air sealing contractors I don't really think that I have access to them. Whoever did the original cellulose upgrade to only the upper attic (homeowners?) put it right up against the furnace chimney so I'm thinking they weren't qualified and I'm glad we haven't had a fire :P The best part is that my home inspector didn't catch it.

  6. davidmeiland | | #6

    I don't know, Kim, but I live in a very small and remote community and there are a handful of us here who do the type of niche work that you need. It's all a matter of digging hard and working your network to find who you need. The fact that there was some hack work done in the house doesn't mean there are no good tradesmen there.

  7. Michael Chandler | | #7

    You may also have one with the "triple wall" chimney that is designed to be cooled by allowing air to constantly flow from the open area above the metal fire box to the exterior. these can be impossible to remediate without replacing the entire system.

  8. davidmeiland | | #8

    Michael, OP states that this is a gas fireplace. Would that venting system still possibly apply?

  9. New2Alberta | | #9

    I don't doubt that there could be good tradesmen that will work here. I have only lived here a year so I don't have much of a network to work yet. The business that it supposed to do our attic insulation is someone I know personally and was recommended by another friend who is a contractor. We also know a few guys with plumbing/HVAC companies I could ask but they tend to be super busy.

    My attic was my priority before it frosts here but with so much air coming in the fireplace I'm wondering if that should be addressed first. The insulation was supposed to happen later this week.

  10. Crazycocobolo | | #10


    Correct me if I am wrong but you have what is likely an old masonry fireplace and chimney with a gas fireplace "Insert" installed into the existing wood burning fire box?

    If this is correct, your problem is unfortunate all to common.

    Please advise and I will try and make recommendations.

  11. leoj100 | | #11

    I would like to resurrect this thread. Hopefully Kim got answers. I would like to hear what she was able to find/fix. I have the same problem but I have some added wrinkles. I definitely have air flowing in near where the gas line enters the fireplace. I have two fireplaces. One for the basement and one for the main floor. I also have a flue out through the roof. Why do I have a flue out the roof if I have direct vent fireplaces? Also I know there isn’t insulation behind the fireplace because when I look through the giant hole for the gas line I can see OSB. Few questions, is there a way to know if I can remove the Vertical flue? What are my options for insulating behind the fireplace?

    Check the attachment for a picture of the back of my house built in 1996.

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