Chimney Problem Symptoms: What Each Warning Sign Means
Find what you are seeing, hearing or smelling. Each entry gives the usual cause, how urgent it is, and the service that deals with it.
By Mark Jason, owner of NWI Chimney Sweep · 34 years of diagnosing these over the phone
Emergencies come before diagnosis
If you smell gas, a carbon monoxide alarm is sounding, or you hear a roaring or see flames or dense sparks from the chimney top, get everyone out of the house first. From outside, call 911, and for a gas odor also call your gas utility’s emergency line. Do not stop to open windows, flip switches or look for the source. Call us afterward, once the fire department or utility has cleared the home.
Which chimney symptoms mean stop using the fireplace?
Stop using the fireplace for five symptoms: smoke entering the room, tile pieces in the firebox, shiny or honeycombed creosote, animals in the flue, and soot on gas logs.
| Symptom | Urgency | Keep using it? |
|---|---|---|
| Smoke rolling into the room | High | No – stop until inspected |
| Pieces of clay tile in the firebox | High | No – stop until inspected |
| Shiny or honeycombed black deposits | High | No – stop until inspected |
| Scratching, chirping or fluttering in the flue | High while occupied | No – stop until cleared |
| Soot on gas logs, or a pilot that keeps dropping out | High for soot; moderate for pilot | No – leave the gas unit off |
| Water or dampness in the firebox | Moderate | Not while wet; fix the leak this season |
| Rust on the damper or firebox | Moderate | Yes, with an inspection booked |
| Crumbling mortar or flaking brick | Moderate, rising each winter | Yes, unless bricks are loose |
| White staining on outside brick | Low to moderate | Yes |
| Strong odor in humid weather | Low | Yes |
| Drafty fireplace when not lit | Low | Yes |
| Dryer needing two cycles | Moderate – a fire risk | Limit dryer use until cleaned |
| Dust puffing from supply registers | Low | Not a fireplace issue |
Symptoms of water getting into a chimney
Water entry shows up as white staining, a damp firebox, rust, crumbling mortar or a musty smell, and it is the most common chimney problem in Northwest Indiana.
White, chalky staining on the outside brick
The white powder is efflorescence: salts dissolved by water moving through the masonry and left on the face when it dries. Usual cause: a cracked crown or open mortar joints letting rain in, or condensation from a gas appliance soaking through from inside the flue. See chimney repair and masonry. Urgency: low to moderate. The salt is harmless, but the water behind it damages brick once it freezes.
Water or dampness in the firebox
Puddles, drips or a damp hearth after rain mean water is travelling the full height of the flue. Usual cause: a missing or undersized cap first, a cracked crown second. Both are covered on our chimney caps and crown repair page. Urgency: moderate. Do not burn in a wet firebox, and have it corrected before winter.
Rust on the damper or firebox
Rust streaks on a damper plate, a prefab firebox wall or a chase cover show the metal has been wet many times, not once. Usual cause: a leak that has run for more than one season, most often from the top of the chimney. A chimney inspection finds where it starts. Urgency: moderate. A rusted-through damper or firebox panel stops being a repair and becomes a replacement.
Crumbling mortar or flaking brick faces
Sandy, receding joints and brick faces that pop off are called spalling. Usual cause: water soaking in, freezing and expanding. NWI winters cross the freezing point many times a season, which is what drives it. Eroded joints are repaired by tuckpointing before the damage reaches the brick. Urgency: moderate and rising every winter. Loose bricks at the top are a falling hazard and make it urgent.
A strong odor in humid weather
A sharp, smoky or barbecue-like smell from a cold fireplace is creosote reacting to damp summer air. Usual cause: deposits left in the flue and smoke chamber, plus air being drawn down the chimney when the air conditioning runs. A thorough chimney sweep removes the source. Urgency: low. It is unpleasant, not dangerous, but it tells you the flue is due for cleaning.
Symptoms that exhaust is not getting out
Smoke in the room, cold air falling from the firebox and animal noises all mean the flue is blocked, leaking or working against the house.
Smoke rolling into the room
Smoke that spills from the fireplace opening with the damper fully open means the flue cannot carry the fire’s exhaust. Usual cause: a blockage such as a nest or fallen tile, heavy deposits narrowing the flue, a flue too small for the opening, or kitchen and bath fans pulling the house into suction. Start with a sweep and a draft check. Urgency: high, because where smoke goes carbon monoxide goes too. Stop using the fireplace until it is inspected.
A drafty fireplace when no fire is lit
Cold air dropping out of the firebox means the damper is not sealing. Usual cause: a throat damper warped by heat or pitted by rust so that it closes on a gap. The modern fix is a gasketed damper at the top of the flue, described under top-sealing dampers. Urgency: low. It costs you heat, not safety.
Scratching, chirping or fluttering in the flue
Noises from the flue mean something is living in it. Usual cause: an uncapped flue. Squirrels and raccoons climb in; chimney swifts nest on the walls in summer and are protected by federal law while nesting, so they cannot be removed until the young have flown. Afterward, a sweep and a properly screened chimney cap prevent a repeat. Urgency: high while the flue is occupied. Stop using the fireplace until it is inspected. Nesting material is both a blockage and fuel.
Symptoms on the flue wall itself
Tile fragments in the firebox and glossy or puffy black deposits are signs that the liner is broken or has already been through a chimney fire.
Pieces of clay tile in the firebox
Thin, curved, terracotta-colored shards on the firebox floor are pieces of the flue liner. Usual cause: a past chimney fire, water freezing inside cracked tile, or age. A broken liner lets heat and gases reach the brick and nearby framing. Ask about chimney relining with a stainless liner. Urgency: high. Stop using the fireplace until it is inspected.
Black, shiny or honeycombed deposits you can see
A glossy, tar-like coating is stage 3 creosote; a puffy, honeycomb-textured gray-black crust is creosote that has already burned. Usual cause: wet wood and slow, air-starved fires for the glaze; an earlier chimney fire, sometimes one nobody noticed, for the honeycomb. Either calls for a Level 2 camera inspection. Urgency: high. Stop using the fireplace until it is inspected.
Symptoms of a worn part or a clogged duct
A pilot that drops out, a dryer that needs two cycles and dusty registers each trace to one worn component or one restricted duct, not to the chimney structure.
A gas fireplace pilot that will not stay lit
A pilot that lights while you hold the button and dies when you let go means the safety sensor is not holding the gas valve open. Usual cause: a weak thermocouple or thermopile (the probe the pilot flame heats to generate a small voltage) or a dirty pilot orifice that keeps the flame off the probe. It is a routine fix during a gas fireplace tune-up. Urgency: moderate for the pilot alone. If you also see soot on the logs or glass, leave the unit off until it is serviced, because sooting means incomplete combustion.
A clothes dryer that needs two cycles
Clothes still damp after a full cycle mean the dryer is making heat but the moist air cannot leave. Usual cause: lint narrowing the exhaust duct, a stuck outside hood flap, or a run longer than the 35 feet (less 5 for each 90-degree elbow) that IRC Section M1502 allows by default. See dryer vent cleaning. Urgency: moderate. Lint is combustible and a restricted dryer runs hot, so limit use until the duct is cleaned.
What to do after you find a symptom
Write down what you saw and when it happens, stop using the appliance if the table says so, and have the chimney inspected before the next fire.
Two or more symptoms from different groups, say white staining outside plus tile shards inside, suggest the problems are connected and should be assessed together so the repair is done once. Timing is the most useful clue you can give a sweep: during rain, in wind, at start-up, or in humid weather.
For checks you can make yourself, use the step-by-step chimney maintenance guide. To see which symptoms your home’s age makes most likely, read the data study of Lake and Porter County housing.
Symptom questions
Which chimney symptoms mean I should stop using the fireplace right away?
Stop using the fireplace if you find tile shards in the firebox, shiny or honeycombed creosote, smoke entering the room with the damper open, animals or nesting in the flue, or soot forming on gas logs. Each of those chimney symptoms means heat or exhaust may not be contained. Leave the fireplace unlit until a sweep has inspected it.
What does a chimney fire sound and look like?
A chimney fire is usually described as a low roar like a freight train, with loud cracking and popping, dense smoke, and flames or sparks from the chimney top. Some chimney fires burn slowly and quietly and are discovered later from the puffy, burnt deposit they leave. If you suspect one is in progress, leave the house and call 911.
Why does my fireplace only smoke on windy days?
A fireplace that smokes only on windy days is usually suffering a downdraft: wind striking the roof or a taller wall nearby pushes air down a short chimney. A chimney that ends too low relative to the roofline is especially prone to it. A wind-rated cap or added flue height usually cures it, once the cause has been confirmed on site.
Is efflorescence on a chimney harmful?
Efflorescence itself is harmless; it is only salt left on the brick surface. What it signals is not harmless: water is passing through the chimney masonry, and in a freeze-thaw climate like Northwest Indiana’s that same water breaks down mortar and brick. Treat white staining on a chimney as an early warning to find the leak.
How can I tell if the animal in my chimney is a bird or a raccoon?
Chimney swifts make a rapid, high chittering that swells when the adults return to feed their young. Raccoons make heavier thumps and a low churring, usually from the smoke shelf just above the damper. Whichever animal is in the chimney, keep the damper closed and do not light a fire to drive it out.
Why does my gas fireplace smell when it first comes on?
A gas fireplace often gives off a brief dusty smell at the first lighting of the season as dust burns off the burner and logs. A smell that persists, a rotten-egg odor or eye irritation is different: shut the gas fireplace off, and if you smell gas, leave the house and call the gas utility from outside.
Can a clogged dryer vent really start a fire?
Yes, a clogged dryer vent can start a fire. Lint is highly combustible, and a restricted duct makes the dryer run hotter and longer. The warning signs come well before ignition: cycles that take twice as long, a cabinet that is hot to the touch and an outside hood flap that barely opens while the dryer is running.
Do I need to be home for a chimney problem to be diagnosed?
Yes, someone needs to be home when a chimney problem is diagnosed. Most of the work happens from the firebox and with a camera inside the flue, so we need access indoors, and we want to walk you through the photos and footage in person before recommending any repair.
Seeing one of these at your house?
Call and tell us the symptom and when it shows up. We will tell you what it most likely is and what to do next.
Call (219) 203-9797