[header] How to cap a chimney [title] Push the cap inside the flue. [step] Position the cap so that it is centered directly over the inner pipe of the chimney. Push down on the cap, using your body weight to apply extra force, until the cap slides into the pipe. 
[substeps] Continue pushing until the solid part of the pipe is completely hidden inside the chimney. The netted or cage-like portion should be elevated above the chimney top.