Understand your chimney
45 plain-English guides on how chimneys work, what warning signs mean and how to weigh repair decisions. Each one answers a single question and is clear about what only an inspection can settle.
How chimneys work
Crown vs. Cap: What's the Difference?
The crown is the concrete or masonry slab that covers the top of the chimney's brickwork and sheds water away from it. The cap is the metal…
Inside the Firebox
A masonry firebox is a chamber lined with firebrick, which is made to handle direct flame, and laid with thin joints of heat-resistant…
Flue vs. Liner
The flue is the open passage inside a chimney that carries smoke and gases out of the house. The liner is the material that forms the walls…
Masonry vs. Factory-Built Chimneys
A masonry chimney is built on site from brick, block or stone, usually with a clay or metal liner inside. A factory-built (prefab)…
The Parts of a Chimney, Top to Bottom
A typical masonry fireplace chimney has three zones. At the top, the cap, crown and flue liner shed water and let smoke out. Along the roof…
Throat Dampers vs. Top-Sealing Dampers
A throat damper is a metal plate just above the firebox that you open and close with a handle or lever. A top-sealing damper is a…
What Is a Smoke Chamber?
The smoke chamber is the funnel-shaped space between the top of the fireplace (the throat and damper) and the bottom of the flue liner. It…
Warning signs
Animals and nests in the chimney
Uncapped chimneys attract raccoons, birds, squirrels and other animals looking for shelter or a nest site. Do not light a fire or try to…
What cracked flue tiles mean
Cracked flue tiles mean the liner may no longer fully contain heat, smoke and combustion gases, so they can reach the chimney masonry and…
Why does my fireplace smell?
Most fireplace odors come from creosote and soot in the flue, and they get stronger in humid weather and when air is flowing down the…
Leaning or separating chimney
A leaning or separating chimney is moving, usually because its footing has settled or failed, or because the upper part of the stack has…
Rust and brown stains on a chimney
Rust-colored streaks running down a chimney usually come from metal above them: a galvanized chase cover on a siding-clad chimney, a…
Signs you've had a chimney fire
A chimney fire can be loud and obvious, or slow and quiet enough to go unnoticed. Afterward, common evidence includes puffy or honeycombed…
Why does smoke come into the room?
Smoke comes into the room when the chimney's upward draft is weaker than the forces pushing air back down. The most common causes are…
Why is my chimney brick flaking?
Chimney brick usually flakes or spalls because water soaks into the masonry and then freezes, expands and breaks off the face. Salts…
White staining on brick (efflorescence)
White, powdery staining on chimney brick is usually efflorescence: water-soluble salts carried to the surface by moisture and left behind…
Why Is My Chimney Leaking?
Most chimney leaks come from one of five places: an uncapped flue, a cracked or poorly built crown, porous brick and worn mortar, failed…
Maintenance
Creosote: Stages, Risk and Removal
Creosote is the residue left on flue walls when wood smoke cools and condenses. It can be dry and flaky, sticky and tar-like, or hard and…
Getting Your Chimney Ready for Heating Season
Before the heating season, test smoke and CO alarms, look over the chimney from the ground, check the firebox, damper and hearth with a…
Burning the Right Firewood
Burn only dry, split, seasoned wood. The U.S. EPA recommends a moisture content of 20 percent or less, checked with a moisture meter on a…
How Often Should a Chimney Be Swept?
Have your chimney inspected once a year, whether or not you used it much. Have it swept when the inspection finds enough buildup to need…
Caring for a Fireplace You Never Use
An unused fireplace still needs attention because the chimney is still exposed to rain, freeze-thaw, animals and air movement. Keep the top…
Inspections
What to do after a chimney fire
After a chimney fire, do not use the fireplace, stove or any appliance connected to that chimney until it has been swept and inspected by a…
Buying a home with a fireplace
When a home changes hands, NFPA 211 as explained by the Chimney Safety Institute of America calls for a Level 2 chimney inspection, which…
What a chimney camera inspection shows
A chimney camera inspection runs a small video camera up or down the flue to show the liner's surface and joints along its full length. It…
Chimney inspection levels 1, 2 and 3
The three inspection levels described in NFPA 211 and explained by the Chimney Safety Institute of America build on each other. Level 1…
Repair decisions
Stainless, Cast-in-Place or Clay Liner?
Stainless steel liners are the most common choice for relining, because they suit most fuels and fit through offsets when the flexible type…
What Affects Chimney Repair Cost
Chimney repair cost depends mainly on the scope of the problem, how hard it is to reach the chimney safely, the materials involved, and…
Do Chimney Sealers Work?
Breathable, penetrating water repellents, such as silane and siloxane products, can help a sound chimney absorb less rain while still…
Crown Coating vs. Crown Rebuild
A crown coating is a reasonable choice when the crown is structurally solid and the damage is limited to hairline cracks, small chips, or a…
Flue Resurfacing vs. a New Liner
Flue resurfacing works on clay tile liners that are still in place but have gaps at the joints or minor cracks and spalling. It keeps the…
Repair or Rebuild a Chimney?
Repair is usually the right call when the damage is limited to the surface, a few bricks, or worn mortar joints, and the chimney is still…
Repointing vs. Tuckpointing
Repointing means removing deteriorated mortar from the joints and replacing it with new mortar. Tuckpointing, in its original sense, is a…
Fireplaces, inserts and stoves
Fireplace Inserts Explained
A fireplace insert is a wood, gas, or pellet heater designed to fit into an existing fireplace opening. Each type vents through the chimney…
Gas Logs vs. Gas Inserts
Vented gas logs are mainly decorative: they sit in an open wood-burning fireplace and send their exhaust up the existing chimney with the…
Oil Furnace and Boiler Flues
Oil furnaces and boilers send soot and sulfur compounds up the chimney. Over a heating season these build up on the flue walls, can…
The Orphaned Water Heater Problem
An orphaned water heater is a gas water heater left as the only appliance venting into a chimney that was sized for a furnace and water…
Factory-Built Fireplaces: Care and Limits
Factory-built fireplaces are metal fireboxes with refractory panels, connected to a matching metal chimney and cap that were tested…
How a Wood Stove Should Be Vented
A freestanding wood stove connects to a chimney through a short connector pipe. The chimney is either a listed factory-built chimney rated…
Homeowner decisions
Chimney Damage and Homeowner's Insurance
Only your insurer and your policy can say whether chimney damage is covered; this guide does not give coverage or legal advice. What you…
Converting a Wood Fireplace to Gas
There are three common ways to convert a wood fireplace: vented gas logs that use the existing chimney with the damper held open, vent-free…
Chimneys on Historic Homes
On older homes, chimney repairs should respect the original materials: mortar that is no harder than the original and softer than the…
Should You Remove an Unused Chimney?
If you no longer use a chimney, you can keep maintaining it, seal and cap it, take it down below the roofline and close the roof, or remove…
Replacing Your Roof? Plan the Chimney Too
Have the chimney inspected before the roof replacement starts, so masonry, crown, and cap repairs can be done first and the flashing can be…