Q: My Flueblocker has gaps around the edges.
I measured my opening of my cast iron damper frame. The opening of the damper frame in the flue is 7″x20″.

So I purchased the 8×24 Flueblocker. I don’t know if I needed a bigger size, or what the issue is, but the seal is poor since my Flueblocker has gaps around the edge. I am including pictures and video of the two biggest gaps, where I can feel the draft come in.


I tried plugging the gaps with other material, but it just made the seal worse and it started to fall down. Any help would be appreciated, even with our top sealing damper and this Flueblocker, the smell inside the house from the draft is terrible. Thank you for your help. – M.U.

A: Dear M.U., Wow! you did a great job with the photos and video showing your Flueblocker has gaps! Thank you!

The right side where your Flueblocker has gaps is pretty easy to fix. The top seal damper cable is causing that. So just take a pair of sturdy scissors and make a small slit in the edge of the wool pad to let the top seal damper cable through.

Flueblocker pulled through the damper

Flueblocker pulled through the damper

The center spot where your Flueblocker has gaps is a little trickier. It looks like the culprit causing the gap is the white mortar that is kind of gooped up on top of the metal frame right there. Sometimes you can use a hammer and a flat head screwdriver to chisel off a chunk of mortar like that. It should release from the cast iron pretty easy.


But, I keep an L-shaped bent wire hanger in my tool kit to help with this kind of situation. I use the hanger as a hook to get behind the wool pad in the spot to bring it forward a bit. Sometimes you even need to actually bring the pad to the front of the frame in that little spot or in the center in general. Like the photo on the left.
Mortar globs are a pain in the butt. In your case it is the reason your Flueblocker has gaps in that center spot. You just have to try a few things to knock them out or work around them.
BTW, since you are trying to stop fireplace smells don’t forget to deodorize the firebox as well. Here is a link on how to deodorize a fireplace: