Can I block the flue if I have a Valor gas insert?

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New Member
Jul 9, 2023
Greenville, Sc
I have a 40+ year old house in the Southeast with a traditional fireplace that was used to burn wood for many years before we bought the house. We have installed a Valor G4 gas insert that performs very well. I understand that these units are self-contained with 2 pipes coming down the flue - one to bring in fresh air and one to exhaust by-product and I assume heat.
Occasionally, due to air conditioning, chimney smoke smell is pulled from the fireplace back into the house. I'm wondering if I can block up the flue with something, such as a sheet of metal or even foam board, obviously with 2 holes in it so the 2 pipes can pass through. Before we had the Valor installed I actually did block up the flue with a foam board (we weren't using the fireplace because it was deemed unsafe for various reasons - thus the insert) and we never had the smoke smell in the house. My concern is that I don't know how much heat radiates or flows up the flue, if any, besides what goes back up one of the pipes. If I block up the flue with a foam board, is there concern of it melting or catching fire? Is there any reason that the flue needs to be open with this type of device or does all the heat go up the pipe? I feel like this is hard to explain but I'm hoping someone understands what I'm asking and has some helpful advice.
Thank you!
Yes you can the best thing would be a sheet metal block off plate with insulation above but just insulation will make a big difference. Use mineral wool insulation like roxul