Asked on Jan 03, 2013

Need Help Closing Off Fireplace

Jeff C
by Jeff C
I find myself in a chilly situation. I discovered this morning that the fireplace damper in the basement fireplace is pretty much rusted beyond repair. The cold 10 degree air has been rushing through the damper hole into the basement and eventually to the upstairs kitchen, etc. Eventually, we heat the air and waste a ton of energy/heat. I need your help/advice on how to effectively seal this fireplace area to prevent as much cold air as possible from entering that space. I have closed the damper to cover the hole to the best of my ability but there is still a good amount of air seeping in around the edges. The only thing I can think of is to stuff the space with some sort of insulation or a giant blanket and then seal off the hole by screwing a piece of plywood over it until one day, we have the funds to fix the darn thing.
For now, I've placed a blanket behind the crappy glass fireplace cover but air is getting in on the bottom corners and such.
  22 answers
  • Google Chimney Balloon - they work great
  • KMS Woodworks KMS Woodworks on Jan 03, 2013
    You could also pick up a sheet of the rigid blue foam from the local home center. a 2 by 8 foot piece, this stuff has a tongue and groove profile so it is pretty tight fitting to itself. using a razor knife cut the pieces to have snug fit in the opening
  • Barb Rosen Barb Rosen on Jan 03, 2013
    My Mom & Dad used to stuff their 1865 home's chimneys (no dampers at all) with insulation pieces left over from insulating the attic. Seemed to do the job!
  • KMS is on the money. I have a customer that used the R-Max sheathing (which is typically used in exterior applications). This is also easy to cut with a razor knife. My customer put this into the opening of their fireplace, then caulked the edges. (This fireplace will not be used, so this is more of a permanent application). She then painted the foil side of the insulation with a very nice mural that fits into the decor of the room. Keep in mind these applications are minimal in insulation (RMax has an insulating quality of R-3.)
  • Jeff C Jeff C on Jan 03, 2013
    I was thinking along the same lines as gluing a piece of 2 inch foam onto a piece of plywood that fits snugly into the opening and then maybe taping the sides.
  • Kimberly Barney Kimberly Barney on Jan 03, 2013
    I realize that money is an issue. However, I hate to see a fireplace become unusable. I've seen several inserts that I feel would allow you to use the fireplace while not having to deal with the cold air entering your home.
  • Check out this web site. They are one of my main suppliers for items such as this.
  • Jeff C Jeff C on Jan 04, 2013
    I'll have to remember that site for next time if I ever encounter a similar situation. For now, I ran out to Home Depot and purchased a piece of 4' X 8' Foam board that has an R value of 10. Because of the size of the hole, I'm able to glue two pieces together to form four inches of foam board glued to a piece of OSB board. It looks like this is going to work although I discovered that the OSB board is a bit too tall and I'll have to cut about three inches from it. After I install the piece, I am going to use some graphite stuff I found at ACE Hardware that allows me to seal gaps but the stuff never hardens. That way, if and when we fix the fireplace, it will be as simple and peeling that stuff off and removing the board with the insulation.
  • Jeff C Jeff C on Jan 04, 2013
    So I finished up the temporary sealing of the fireplace. As I explained earlier, I took two pieces of 2 inch R-10 foam board and glued them together. I then took a 4X4 piece of OSB board and glued the insulation onto the board. I then placed the board against the fireplace bricks so that the two pieces of insulation fit right inside the opening. I then placed two tapcon screws, one in each corner to hold the board tightly against the brick. I then used this really sticky duct work stuff to seal around the edges of the plywood. This stuff doesn't harden so when we decide to fix the fireplace, it will be as simple as removing the board and peeling away the sticky stuff. I can already feel a noticeable difference in temperature thanks to the board covering up the hole.
    comment photo
    comment photo
    comment photo
    comment photo
    comment photo
  • Curtisev Curtisev on Jan 04, 2013
    A roll of insulation the diameter of the flue plus 4", jamb it up there. Or four smaller rolls to get around the damper. Display something in that nice fireplace. I put my flat screen TV in front of it.
  • Jeff C Jeff C on Jan 05, 2013
    Trust me, no one would want to be watching TV in my basement. I refer to it as the dungeon for obvious reasons.
  • Jeanette S Jeanette S on Jan 05, 2013
    A fireplace is great for atmosphere, but we have found it worthless in a crunch. Fireplaces just do not heat well and gas logs are worthless. Follow KMS's advice and close it off. Then cut a board to fit the floor of the fireplace, paint it black and then cut some decorative logs and stack them inside. It will be pretty but you do not have to use it.
  • Jeff C Jeff C on Jan 05, 2013
    I've been trying to convince my wife that a pellet stove or something to that effect would be much more efficient than a wood burning fireplace but she makes fun of me about the idea of pellets and my parents like the atmosphere with sitting around a fireplace with real burning logs. To me, it just means more hassle, having to make sure I have dried wood every year and then getting the fire place cleaned. I'd like to get something that spreads the heat into the room and perhaps, adjoining rooms.
  • One quick question on this fireplace. You said it was in the basement? Do you only have one? Or is there one on the first floor as well? If so be sure to check carefully that the flues are not connected in any fashion. At all. If they are, you need to have a professional seal off the basement one with cement or fix the damper. Even if the flues are connected together at the top with a single chimney cap. Hot ashes can come back down and catch the back side of the foam on fire. This is more likely to happen when your heating system or if your clothes dryer is in basement running. I was concerned when I saw your photo of the fireplace. I saw soot spillage in the front indicating poor draft. This can be caused by a missing or broke damper and by negative air pressures from the appliances running pulling make up air down backwards in the flue. Be very careful with this and check the flue and if the chimney is connected even with the spark arrest/chimney cap if you have two fireplaces. Seal it either at the top or with cement at the flue damper location.
    comment photo
    comment photo
    comment photo
  • KMS Woodworks KMS Woodworks on Jan 05, 2013
    A free standing wood stove would be my choice for this ...Stainless duct work can be routed through the masonry flue and there by be isolated from the other fireplace (if present)
  • And units can be purchased with blowers included that will push that heat out into the basement (in this case) and into the home.
  • Rebekka Rebekka on Jan 02, 2016
    A piece of thick foam cut larger than the chimney can be wedged up there to close it off. No board necessary! Just make sure that it is removed before anyone starts a fire!
  • Judy Judy on Sep 19, 2016
    I closed off a fireplace in a rental a few yrs ago. I had a large piece of foam board, that I cut just the right size to insert over the fireplace and secured it with packing tape. Worked great for 2 yrs before I moved.
  • We28518635 We28518635 on Oct 14, 2016
    All great answers and I would also put a heavy blanket on the inside of the glass and then put some heavy piece of furniture in front of the fireplace our last resort (if you don*t use the fireplace is to take down the chimney on the roof and then cover that hole with new plywood and roofing tiles to match your roof.
  • Insulation foam or just the roll should help.

  • Deb K Deb K on Nov 02, 2022

    Hi Jeff, hope this helps you out. you could use rigid foam insulation to cover the opening.

    comment photo
  • Mogie Mogie on Nov 04, 2022

    Don't forget to cap the top of the chimney also.