Why is water leaking from my chimney damper?
Short answer. Water at the damper almost always enters from the top of the chimney rather than the roof flashing: a missing or damaged cap, a cracked crown, a gap around the flue liner, or, on framed chimneys, a rusted chase cover. Condensation in a cold flue and rain soaking through the masonry are the other common causes.
Why the damper collects water
The damper is the lowest closure in the flue, so anything that gets into the top of the chimney ends up sitting on it. A rusted damper plate, rust flakes in the firebox, or water dripping from the damper handle are the classic signs.
Likely sources
- No chimney cap: an uncapped flue is an open pipe to the sky, and rain, leaves and animals come straight down.
- Cracked or poorly built crown: the concrete top should slope away from the flue and overhang the brick. Cracks, or a thin flat mortar wash in place of a real crown, let water into the chimney's core, where it runs down inside.
- Gap around the flue liner: the joint between the liner and the crown opens up over time.
- Chase cover on a framed chimney: the metal cover on top of a sided chimney rusts or sags, pooling water that drips down beside the metal flue.
- Condensation: in cool weather, moist air in an unused flue condenses on cold surfaces and drips onto the damper, especially when gas appliances vent into the same chimney.
- Saturated masonry: old brick soaks up wind-driven rain, and the water migrates inward.
What to do
- Look at the chimney top with binoculars, or from a drone photo, and check whether there is a cap and whether the crown is cracked.
- Note whether the dripping follows rain or happens on dry, cool days.
- Have the fireplace inspected before using it again if the damper is rusting.
Cap, crown and liner repairs are chimney and masonry work. If there is also a stain on the ceiling or wall beside the chimney, the roof flashing may be leaking too. See chimney leaks and crickets and common roof leak causes.