Q: Jason, I have a set of vent free gas logs in my fireplace. The fireplace also has a regular 18″ round chimney flue and a round metal flapper damper. If I understand correctly most vent free gas logs do not have a chimney since they are supposed to vent into the house directly to provide all the heat to the living area.
The damper on this ventless gas log fireplace chimney is worn out and lets in noise and cold air when the fireplace is not being used. Can I install a Chimney Balloon above the damper and close the damper and keep the Chimney Balloon in place even during the time I use this ventless gas log fireplace? – KK
A: Dear KK, We get a lot of questions about using a Chimney Balloon with gas log fireplaces. Especially about ventless gas log fireplaces that have chimneys. Most vent less (or vent free) gas log fireplaces do not have chimneys or flues in the first place. They are often designed to vent directly into the living area. This does allow them to give all of their heat to the living area, but it also allows them to give all of their fumes and moisture to the living area as well. For this reason I am not too keen on vent free gas logs.
To get to your question about the Chimney Balloon and if you can use it above your damper on this vent free gas log. You said your damper is leaking in cold air and noise from the outside and the damper is not in good shape. This means the leak goes both ways on your damper. Cold is coming in and heat certainly going out both during your fireplace use and when the fireplace is dormant. The Chimney Balloon is designed to shrivel and release when heat or fire is introduced to it. This release mechanism triggers at about 180 to 220 degrees. The Chimney Balloon does this because it is designed to plug the chimney flue, and in most cases it is not desirable to have a plugged chimney flue when you have a fire in your fireplace.
So if you light a fire in your ventless fireplace and the Chimney Balloon is installed above your damper (even with the damper closed) the damper itself will heat up and conduct heat through. As you said, the damper is also leaky since it allows cold air down, it will also allow heat up as well. That heat will come in contact with the Chimney Balloon. This will certainly trigger the release of the Chimney Balloon sooner or later (probably sooner). Then you will have a cooked Chimney Balloon. It is still worth it to have the Chimney Balloon in place in your fireplace when you are not using this vent free fireplace since it will eliminate the cold air and noise issue, but you cant leave it in place during use of your fireplace.
I have had many people ask: “what is safe to use above a ventless gas log to plug the flue?” Some people use safing insulation to plug the fireplace flue above a ventless gas log. I realize safing insulation is fire retardant, but safing insulation is not made for this specific purpose so this is a risky venture at best. – Jason