Q: Dear Jason, Do you make a Chimney Balloon for a 10.5″ diameter, circular chimney uptake?  Your products seem to be made of squares or rectangles.  I can’t put a square into a round hole and expect a snug fit…or can I?  Thank you. RM

A: Dear RM, Thank you for your Chimney Balloon question. You present a very common question about the Chimney Balloon. How can you fit a square or tapered Chimney Balloon into a round hole (like a round metal flue)? The answer is… Chimney Balloons are flexible and only expand as far as the flue wall allows it to and no further, the extra material either folds or pops inward and the Chimney Balloon is still able to seal tightly.

We have a tradeshow demo that we use to explain it and I took two photos of the demo, so you can see what I mean. This image is a 9″ clear tube with a 9×9 Chimney Balloon installed in it. Your 10.5″ diameter flue would need a 12×12 Chimney Balloon, but it will seal the same.

However, if you really want to get around 12″ Chimney Balloon we do make those as a custom for the same price as the standard, it just takes 14 days to get a custom made and shipped to you. The rounds are not listed on the website, so you would need to call in the order and we can enter the order indirectly with proper build notes. – Jason