How to position and measure:
Measure your chimney about a foot or so out of sight where your Chimney Balloon will fit as shown in the diagrams. You will need the side to side and the front to back inside dimensions. We suggest you use a flexible steel tape measure (Stanley type) or two pieces of wood or cardboard extended like wings. It is only necessary to measure approximately and choose the Chimney Balloon of the appropriate size or slightly larger than your chimney. You can always just count the bricks inside - allow 9 inches per brick length.