How Often Should You Clean Your Chimney?
Inspect a chimney every year and sweep it once soot reaches 1/8 inch; here is how that works for wood, gas and furnace flues.
Have your chimney inspected once a year, and swept whenever that inspection finds 1/8 inch of soot or any shiny, glazed creosote. That is the NFPA 211 standard and the Chimney Safety Institute of America guideline. For most homes that burn wood regularly, it works out to one sweep a year.
How often does a chimney need cleaning?
A chimney needs cleaning when the deposits inside reach about 1/8 inch, and it needs an inspection every year to find out whether they have. NFPA 211, the national standard we work to, says chimneys, fireplaces and vents shall be inspected at least once a year, with cleaning, maintenance and repairs done if necessary. The Chimney Safety Institute of America (CSIA) puts a number on “necessary”: sweep a masonry fireplace at 1/8 inch of sooty buildup, and sooner if there is any glaze. The U.S. Fire Administration keeps it simpler and advises having chimneys cleaned and inspected each year by a professional.
So the calendar sets the inspection and the soot sets the sweep. In our view, if you burn wood regularly through the winter, plan on a chimney sweep every year.
Why is 1/8 inch the line?
An eighth of an inch is the point where, according to the CSIA, fire safety experts consider there is enough fuel in the flue to feed a chimney fire that can damage the chimney or spread to the house. That fuel is creosote, which is what is left behind when wood smoke cools and condenses on the flue walls. It ranges from loose, dusty soot to a hard, shiny glaze.
Glaze is the reason the guideline says “sooner”. A brush will not take it off, so it needs a separate creosote removal treatment. Factory-built (prefab) fireplaces have a stricter rule again: the CSIA says to sweep them when any appreciable buildup occurs.
How often should you clean a chimney based on how you use it?
The inspection is yearly for everyone, but how often it ends in a sweep depends on what you burn and how much. This table is our rule of thumb.
| How you use it | Inspection | Sweep |
|---|---|---|
| Wood fireplace, used most weeks in winter | Every year | Expect one every year |
| Wood stove or insert used for heating | Every year | Expect one every year; check mid-season if you burn daily |
| Wood fireplace, a handful of fires a year | Every year | When buildup reaches 1/8 inch |
| Gas fireplace or gas logs | Every year | Rarely needs brushing; needs servicing |
| Furnace or water heater flue | Every year | Only if the inspection finds a blockage or deposits |
What makes a chimney need cleaning more often?
Anything that makes a fire smoke more, or makes the flue run cooler, builds creosote faster. These are the usual causes:
- Wet wood. The EPA’s Burn Wise program says wood burns best below 20 percent moisture and should be seasoned for at least six months.
- Smoldering fires. Shutting the air down to make a load last overnight gives a slow, smoky burn.
- A cold flue. A chimney on an outside wall stays colder, so more smoke condenses before it gets out.
- Heavy use. A stove that runs all day puts more smoke through the system than a fireplace lit on weekends.
What are the signs a chimney is overdue for a sweep?
The clearest sign is buildup you can see: black flakes dropping into the firebox, or a dark, crusty or shiny coating on the damper and the flue walls above it. Other signs are a strong tar smell, smoke drifting into the room, and fires that are harder to start than they used to be.
If you think the chimney is on fire. A loud roaring or rumbling from the flue, or flames or dense smoke coming from the top of the chimney, is an emergency. Get everyone out of the house and call 911.
Not sure when your chimney was last swept?
Call (816) 239-8989Does a gas fireplace or furnace flue need the same schedule?
It needs the same yearly inspection, but it usually does not need the same brushing. Gas burns far cleaner than wood, so there is little soot to remove. The CSIA still recommends annual inspections for every chimney, gas furnace flues included, because bird nests and debris can block them, and a blocked flue can push carbon monoxide back into the house. Our gas fireplace service starts at $159.
If a carbon monoxide alarm sounds, get outside and call 911. If you smell gas, leave the house and call your gas utility from outside.
When is the best time of year to have a chimney cleaned?
Spring or summer is the best time, in our view, because any repair the inspection turns up can be finished long before you want a fire. Fall works too, as long as the sweep happens before the first fire of the season rather than after it.
What does a yearly chimney cleaning cost?
Our chimney sweep with a Level 1 inspection starts at $199. If you only want to know whether the flue needs sweeping, a Level 1 chimney inspection on its own starts at $119. The full list is on our pricing page.
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Common questions
How many fires can you have before cleaning a chimney?
There is no reliable number of fires, because buildup depends on how the wood burns rather than how many times you light it. A few slow, smoky fires with damp wood can leave more creosote than a whole season of hot fires with dry wood. The measure that matters is thickness: the Chimney Safety Institute of America says to sweep a masonry fireplace at 1/8 inch of sooty buildup, or sooner if there is shiny glaze. A yearly inspection is how you find out where you stand.
Do I need to clean my chimney if I only use it a few times a year?
You may not need a sweep every year, but you still need the yearly inspection. NFPA 211 calls for chimneys, fireplaces and vents to be inspected at least once a year, with cleaning done only if it is needed. Light use can still leave deposits, and animal nests, loose masonry and water damage have nothing to do with how many fires you burn. If the inspection finds less than 1/8 inch of soot and no glaze, the sweep can usually wait.
How can I tell if my chimney needs cleaning without going on the roof?
With the fireplace cold, open the damper, shine a bright flashlight up the flue and scratch the wall above the damper with a fireplace poker. If the groove you leave is about 1/8 inch deep, or the surface is black, shiny and hard, it is time for a sweep. Black flakes in the firebox, a strong tar smell and smoke drifting into the room point the same way. This check only shows the bottom of the flue, so it does not replace an inspection.
How often should a wood stove chimney be cleaned?
Plan on at least once a year, and check it partway through the season if the stove is a main source of heat. In our view, stoves need closer watching than open fireplaces because they are often run with the air turned down for long, slow burns, and that cooler smoke leaves more creosote in the pipe and flue. Burning wood below 20 percent moisture, which is the EPA Burn Wise guidance, and giving the fire enough air both slow the buildup.
What happens if you never clean your chimney?
Creosote keeps building until it either catches fire or narrows the flue enough to hurt the draft. A chimney fire can damage the chimney and can spread to the house. A restricted or blocked flue sends smoke and carbon monoxide back into the room instead of outside. Skipping inspections also means small problems, such as a cracked crown or a missing cap, go unnoticed until they turn into water damage. If you ever suspect a chimney fire, get everyone out and call 911.