Why Is Water Dripping Into My Fireplace?

How rain reaches the firebox

A fireplace flue is a vertical pipe open to the sky. Without a cap, every rainstorm pours straight down it, and in wind-driven rain the water hits the inside walls and runs down to the damper and the hearth. A typical flue opening catches more water in a heavy storm than most people expect.

Even with a cap, water can get in at the crown, the slab of concrete or mortar around the flue on top of the chimney. A crack in the crown, or a crown with no overhang, lets water into the gap between the flue tiles and the brick. It then works its way down and shows up as drips at the damper or a dark, wet patch on the back wall of the firebox.

The usual causes, most common first

On the older chimneys we see across the region, the causes line up in a fairly steady order. More than one is often involved, which is why a cap alone does not always end the drip.

• No cap, or a cap that has rusted through or blown off
• A cracked, crumbling or flat crown on top of the chimney
• Gaps at the joints between flue tiles
• A rusted damper plate or frame that lets water drop past it
• Porous brick and open mortar joints above the roof

Signs to look for after a storm

Open the damper with a flashlight once the rain stops. Water marks running down the flue walls, rust flakes on the hearth and ashes that have turned into a gray paste all tell you water came down from above. White streaks on the firebox walls are minerals left by water moving through the masonry.

Listen too. A steady drip you can hear inside the fireplace during heavy rain, with no stain on the wall or ceiling around the chimney, is a strong sign the problem is the cap or the crown rather than the flashing. Water on the ceiling beside the chimney points to the flashing instead.

• Drips or puddles in the firebox: missing cap or cracked crown
• Wet back wall of the firebox: crown or flue tile joints
• Rust on the damper and hearth: water coming down the flue
• Stain on the ceiling beside the chimney: flashing at the roof line
• Damp chimney breast upstairs: brick, joints or crown

Why a little water is a big deal

Water mixed with soot and creosote is acidic. It eats the steel damper, stains the firebox and breaks down the mortar between the firebrick. A rusted damper that no longer closes then lets cold air and more water into the house, and a damper plate that rusts through can drop into the firebox.

In Northeast winters, water that sits in the masonry freezes and thaws over and over. That pushes flue tiles and crown cracks further apart each season, so a drip this fall can mean loose tiles or crumbling brick a few winters later. Wet masonry inside the fireplace also holds a musty, smoky smell that drifts into the room in humid weather.

What a technician checks

The inspection starts on the roof: whether every flue has a cap and whether it is the right size and fastened down, the crown's condition and slope, and the brick and joints above the roofline. Then the flue is examined from the top or bottom for open tile joints and cracked tiles, and the damper and smoke chamber are checked for rust and water damage.

If the chimney has more than one flue, each one is checked, since an uncapped boiler or unused flue next to the fireplace flue can feed water into the same masonry.

A water test with a hose, run on one part of the chimney at a time while someone watches the firebox, is sometimes used to confirm the entry point when the visual signs are unclear. It is done carefully and from the roof by the crew, not by the homeowner.

Fixing it from the top down

Most of these leaks are stopped at the top of the chimney. A stainless steel cap with a mesh screen keeps rain and animals out of the flue. A cracked crown is sealed if the damage is small, or rebuilt so it slopes water away from the flue and overhangs the brick with a drip edge.

If the damper has rusted out, it is repaired or replaced, or a top-sealing damper is fitted that also closes off the flue at the top. Cracked flue tiles may need repair or a liner. Because more than one cause is often involved, the whole system is looked at before any one repair is suggested, and the estimate should say which parts address which entry point.

Leaks around inserts, stoves and lined flues

A fireplace with an insert or a stove connected to a liner can leak in its own ways. If the liner was dropped into the chimney without a top plate sealing the old flue around it, rain runs down the outside of the liner and collects behind the insert's surround or on the smoke shelf. Water may then appear at the bottom of the surround panels or as rust on the insert's top.

A cap that fits the liner but not the flue opening, a top plate that has pulled loose from the crown, or a storm collar missing where a pipe passes through a chase cover all do the same. The fix is at the top: a sealed plate, the correct cap and a sound crown. With a gas insert, water can also corrode the burner and valve, so a leak is a reason to have the appliance checked as well as the chimney.

What to do until it is repaired

Do not light a fire on wet ashes or over a soaked firebox; steam can crack firebrick and wet creosote smokes badly. Scoop out the wet ash, wipe down the hearth and let the fireplace dry with the doors open and the damper closed. Put a tray down if the drip is steady, and check it after each storm.

Keep off the roof. Chimney tops are high, steep and slippery when wet, and a pair of binoculars from across the street will show you whether the cap is there and whether the crown looks cracked.