How does chimney cap installation actually work?
It starts with measurements, because caps are not one-size-fits-all. The pro measures the flue tile's outside dimensions — or the whole crown, for a multi-flue cap — and checks what kind of appliance vents through it, since wood, gas, and oil flues have different requirements. Material matters: stainless steel and copper last decades, while lightweight galvanized caps tend to rust out. The mesh sides do double duty as a spark arrestor and an animal barrier, and mesh opening size is a real specification: too coarse lets small animals in, too fine can clog with creosote in wood-burning flues or trap freezing rain in cold climates.
Installation itself is straightforward when done right: single-flue caps clamp or screw to the flue tile, and multi-flue caps anchor into the crown with masonry fasteners, with enough height above the flue that draft is not restricted. One step matters before any cap goes on: confirming nothing is living in the flue. Chimney swifts are federally protected under the Migratory Bird Treaty Act, so an active nest cannot be removed — capping waits until the birds leave on their own, usually by early fall. Raccoons and other animals call for a licensed wildlife operator, never smoke or fire. Expect photos of the finished cap, the product and metal specified in writing, and any manufacturer warranty passed along to you.