Any fuel-burning appliance in your home needs to be properly vented to the outside. This can be accomplished through a chimney liner, which is installed inside the chimney flue to safely contain combustion gases until they are exhausted through the top of the chimney. Fuel-burning appliances that require proper venting include wood stoves, wood-burning fireplace inserts, fireplaces, gas-fired boilers and furnaces, and gas-fired water heaters. If you use a gas range or cooktop in your kitchen, you should also have a properly vented range hood or exhaust fan to remove cooking fumes and combustion products from the home.
Gas-fired appliances are often vented through dedicated metal piping that leads directly to a roof vent, but they can also be connected to a properly sized flue running through a chimney. Combustion gases from fuel-burning appliances can be corrosive because they contain water vapor, carbon dioxide, and other byproducts. For this reason, it is essential that the chimney liner or vent piping be made from materials capable of withstanding the conditions produced by the specific appliance.
Older homes with masonry or brick chimneys may not have dedicated liners inside their flues. Instead, they rely on the condition of the bricks and parging (mortar) to contain combustion gases and prevent corrosive moisture from penetrating the chimney walls and reaching the surrounding structure. These chimneys should be inspected regularly. If an inspection reveals damage caused by corrosive gases, water infiltration, structural settling, chimney fires, or other factors, the chimney should be repaired and the flue lined with a suitable, durable material to help prevent further deterioration.
Several materials are commonly used for chimney liners, including special mortar mixtures, clay tile, and metals such as stainless steel and aluminum.
The type of chimney liner you should install depends on the type of appliance that will be vented through the flue:
- Clay tile liners and poured mortar liners are suitable for many traditional fireplace applications.
- For natural gas or oil-burning appliances, a properly sized metal liner is often the best choice.
- Flexible aluminum liners are an economical option, but they should generally be used only with compatible lower-efficiency gas appliances. These appliances produce hotter exhaust gases, which can help keep combustion byproducts in a gaseous state as they exit the home and reduce prolonged exposure of the aluminum to corrosive condensation.
- For high-efficiency gas furnaces and other high-efficiency appliances, the chimney liner or vent piping should be made from a corrosion-resistant stainless steel alloy specified for the application. Because these appliances transfer more of the generated heat into the home, their exhaust gases are cooler and more likely to produce condensation inside the venting system. Continued exposure to corrosive condensate can damage aluminum or masonry liners and significantly reduce their service life. Many woodstoves and wood-burning fireplace inserts are designed to use stainless steel liners in the diameter specified by the manufacturer.