Why does my fireplace smell musty after it rains?
A musty smell after rain almost always means water is getting into the chimney and wetting the masonry, soot or firebox. The damp material gives off the smell, and air moving down the flue carries it into the room.
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The smell is the symptom, not the problem. Water that finds its way in once will keep doing so, and the entry point is usually the crown, the flashing, a missing cap or worn mortar joints.
Why it happens
Brick and mortar absorb water. When the crown on top has cracked, the flashing where the chimney meets the roof has lifted, or the mortar joints have worn away, rain gets into the structure instead of running off it. With no cap on the flue, rain can also fall straight down the flue.
Once the masonry or the inside of the flue is wet, old soot and creosote deposits take on moisture and give off a sharp, stale odour. Air then moves down the flue into the house and brings that smell with it. That is why the smell is strongest during and just after rain and fades as things dry out.
Left alone, the damage spreads. A chimney that has been wet for years can become structurally unsound, and falling brick is a hazard at the base. A damp patch on the ceiling or wall beside the chimney is another sign that the same water is travelling further in.
What you can check yourself
Note when the smell is strongest
Is it only during or after rain, or all the time? A smell that comes and goes with the weather points to water entry.
Look at the walls and ceiling nearby
Check the surfaces around the chimney breast, and the ceiling above it, for stains, peeling paint or a damp patch.
Shine a torch into the firebox
From the front of the fireplace, look for water marks, damp soot, rust on the damper or debris that has washed down. Do not reach into or climb up the flue.
Look at the chimney from the ground
Use binoculars if you have them. Look for crumbling mortar, flaking brick, white powdery staining or brick fragments at the base. Do not go on the roof.
Test your alarms
Make sure your smoke and carbon monoxide alarms work. This is a good habit with any fireplace.
When to call a technician
The smell is worth a visit even if nothing else looks wrong. The leak path is hard to judge from the ground, and the repair is cheaper and simpler before the masonry has soaked for a long time. Book sooner if you see a ceiling stain, crumbling brick, or debris in the firebox after rain.
If smoke ever comes into the room, stop using the fireplace until it has been inspected. If anyone has a headache or feels dizzy, get outside and call 911. For the musty smell on its own, call One Call Chimney on (866) 576-7943. We arrange a visit from an independent sweep or mason. The estimate is free, the technician inspects the chimney and gives the price before any work starts, and you approve it first.
Permit rules for masonry repairs differ by city and county. If the work is more than a minor repair, check with your local building department.
What the technician will do
- Trace the entry pointThe technician finds where the water gets in, rather than sealing over the stain. Ask to see photos or camera footage of what they find.
- Repair the flashingFailed flashing is replaced and counter-flashed into the mortar joint so water runs off the chimney instead of behind it.
- Repair or recast the crown and fit a capA cracked crown is repaired or recast, and a cap is fitted so rain cannot drop straight down the flue.
- Repoint and replace damaged brickWorn mortar joints are repointed and spalled brick is replaced where the face has broken away.
- Apply water repellent where it suitsWhere appropriate, a breathable water repellent helps the masonry shed rain while still letting it dry out.
Related questions
- Will the smell go away if I just air the room out?
- It may ease for a while, but it will come back with the next rain if water is still getting in. Fixing the entry point is what removes the cause.
- Does a musty smell mean there is mould in the chimney?
- It can mean damp masonry, wet soot or mould growth nearby. A technician can tell by looking at the firebox, the flue and the surrounding walls.
- What affects the cost of fixing a chimney leak?
- The main factors are how easy the chimney is to reach, its height, what the inspection finds, and whether the crown, flashing, mortar or brick all need work. Call (866) 576-7943 for a free estimate, with the price agreed before work starts.
- Can a chimney cap stop the smell?
- A cap keeps rain out of the flue and often helps, but it will not cure a cracked crown, failed flashing or open mortar joints. The technician should check the whole chimney, not just the top of the flue.
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