Fireplace - how to cover control air flow up the chimney

7 Replies

I have a flu that does not seal well on a fireplace.  I have a gas log that I am pretty sure does not need a vent.

I can feel a draft up the chimney.  What would be an inexpensive way to seal it?  I still would like to be able to light the gas fire every once in a while.

@Kirk R.  

If you are burning gas/wood/coal, etc, then you need both a vent (traditionally air from the room) and an exhaust (the chimney) - this is the draught you feel.   Modern gas stoves and fireplace inserts are sealed (airtight) with respect to the living space (room) and vent their combustion air from outside - typically a separate pipe through the side of the building or a centre pipe within the exhaust flue (either through the side of the building or as a sleeve in an existing chimney.

The cheapest way to stop air and heat from being drawn up your chimney is to decommission your fireplace; stuff insulation in the top of the firebox against the closed damper; then tape a sheet of 6mil poly (vapour barrier) under the insulation being certain to create a seal with the sides of the firebox all the way around the perimeter of the barrier.

Since you still want to use your fireplace periodically, but do not wish to incur the expense of installing an airtight insert, you could still attempt to plug the top of the firebox when you are not using the fireplace.   To do this you could cut a piece of rock wool insulation (ether batt or board) to tightly fit into the top of your firebox - I would leave a piece of {bright coloured} string or chain hanging down to remind you the flue is blocked.  When you want to use the fireplace, remove the insulation.  When are have finished and the firebox has cooled, close the damper and replace the insulation.   It will not be as airtight as above, but better than your current situation.

@Roy N. 

Thanks Roy for the input.  I ended up doing a little bit similar to what you said.  A fireplace balloon from HD was like $55.  So I used black garbage bags and double bagged some of that mattress memory foam and shoved it up in in the hole on either side of the handle for the flue.  I can already tell a difference.  

So far for Energy efficiency this year:
Blocked the fireplace mostly - not perfect for sure.
Put that plastic they sell to go over the windows
Caulked one window that was leaking pretty badly.
Put insulation in one of my attic access areas.

Only thing left on my list is one more attic access area.

Hoping I can write some of this off using US 2014 energy tax incentives.  & it's 13 degrees here tonight! so definitely feels warmer than last year.


That should help stop the draught.  However, I still would suggest trying to find a piece of rock wool insulation (such as Roxul Safe-n-Sound) to use instead of the mattress foam (you do not need an entire bail, just part of a single piece).  The rock wool is non-combustable, thus if someone inadvertently lights a fire you will not run the risk of a chimney fire.

In addition to caulking the outside of your windows (which is it now too cold to continue), you can apply a bead of painters latex along the seams of your window boxes (and door frames) and trim to cut down on draughts.    It's cheap ($2 per tube).

Another thing you can do is put foam gaskets behind your receptacle and switch plate covers on all exterior walls - this will reduce the draught and heat loss through the hole into the wall cavity.  You can purchase pre-cut packages of these gaskets at the big box stores - or you can save a lot by purchasing a sheet/roll of the foam gasket and using a receptacle and switch cover to cut out your own.

As for the attic hatches, most of the time there is only a minimal skirt around the inside of the hatch opening.  We usually build the skirt to be 12" high.  We then line the lip of the skirt with a compressible piece of weather stripping (like what you would use around an exterior door stop).  When the hatch drops into the hole, it sits on this weather stripping and compresses it to form a tight seal.   Do do this, the hatch has to have a little weight to it.   We cut sections of rigid foam insulation (scraps from another job) to the size of the hatch and glue them to the topside of the hatch like a layer cake such that the top of the insulation is at, or just above, our new (12" high) skirt when the hatch is in-place.  We then cut a piece of flexible rubber 2 - 3" larger than the rigid foam squares - large enough that, when glued to the top of the stack of foam, it extends out past each side far enough to cover the top edge of the skirt around the attic access hatch.   This forms another draught barrier at the top of the hatch and adds weight to the hatch to help compress the weather stripping on which it sits.   Old (or new) car mats work well as the rubber on the top of the hatch stack.

@Kirk R.  

My edit time on the last post expired.

Instead of using a piece of rubber on the top of the insulation stack on the hatch cover, you could simply cut an additional, larger square of rigid foam insulation which will sit on the top of the hatch skirt.   To add the weight necessary to compress both this top piece of foam and the gasket around the base of the hatch, you could cut a piece of 3/4" plywood and glue (PL 300) it to the top of the larger foam square.    You attic hatch will now be a sandwich of rigid foam (14 - 16" pending on skirt height) between two pieces of 3/4" plywood.

This guide from Uncle Joe provides a good example of an attic hatch and provides you lots of additional guidance on air sealing and insulating your attic.

Instead of going through all that, have you thought about a sliding glass face to the fire place. It will not make it ain't tight but it will greatly reduce the draft and add a nice look.

@Roy N.  Definitely will be doing some of the things you suggested & will try to post couple pics.  5 degrees here now grrr i mean brrrr.

@Joseph Catalano  Hi Joe.  How much could I get a glass cover for?  I put in the gas fake log fireplace.  I kind of wish I would have put in an insert that would have allowed me to heat my place.  Except they are like $1,000. Fireplaces are pretty much a pain in the arse.

@Kirk R.   It should only cost a few hundred dollars but it will add a great look

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