Fireplace dampers are inefficient due to warping and misalignment from frequent heating and cooling. A bad or missing damper can cost you up to 30% more on your heating bill. Your fireplace damper is releasing your indoor heat and letting in cold outside air! The Chimney Balloon is a inflatable stopper that prevents drafts from a chimney caused by a broken, warped, or missing flue damper. It even works in chimneys that have no damper! The Chimney Balloon stops this heat loss by acting as a stopper to insulate your fireplace and save you money, heat, and comfort. This 12"X12" Chimney Balloon is designed to work on a chimney with maximum flue or damper dimensions of 12"x12". It can be used in either a square or a circular chimney. See image link above on how to measure your fireplace for a Chimney Balloon. Every fireplace and chimney is unique, don't be fooled by one size fits all solutions. We list the most commons size Chimney Balloons on Amazon, but Chimney Balloons are available in many sizes. Call Customer Service at 608-467-0229 if you have questions on sizes or measuring your fireplace.