Do I need a chimney cap?
Short answer. Most chimneys should have a cap: it keeps rain from pouring down the flue, blocks birds, squirrels and raccoons, and on wood-burning fireplaces it catches embers. The main exceptions are a flue that has been professionally sealed and taken out of service, and a factory-built chimney that must use the specific cap listed by its manufacturer.
What a cap prevents
- Rain down the flue. An uncapped flue sends rain straight to the damper and firebox. Water mixes with soot into a smelly, acidic slurry, rusts dampers and breaks down clay flue tiles and mortar over time.
- Animals. Squirrels, raccoons and birds nest in open flues. Chimney swifts, a protected bird, nest in uncapped chimneys during Georgia summers and cannot be disturbed while nesting, so cap after they leave in fall.
- Debris. Leaves and pine needles collect on the damper and can block the flue.
- Sparks. A mesh screen catches embers before they land on the roof or in dry leaves.
When the answer is different
- Factory-built chimneys are tested as a system, and the manufacturer's listed cap is part of that system. Do not swap in a generic cap.
- Gas appliance vents need the termination cap designed for that vent so they draft properly.
- Sealed, unused flues may have a solid top plate instead of a cap.
- Top-sealing dampers combine a cap and a damper at the top of the flue, opened by a cable from the fireplace.
Choosing a cap
Stainless steel or copper outlasts galvanized steel, which rusts and streaks the crown. The mesh should stop animals without clogging with soot, so ask your sweep what suits your appliance. A cap that covers the whole crown also shields the crown from rain. The cap protects the top of the chimney and the flashing protects the bottom, so check both, as described in chimney leaks and crickets and the roof maintenance checklist.