Wood heating is a popular and effective auxiliary heating source for homes. However, wood stoves and fireplaces can cause indoor air pollution and fire hazards. Inspect wood stoves to evaluate potential hazards.
Stoves that are listed by a testing agency like Underwriters Laboratory have installation instructions stating their clearance from combustibles. Unlisted stoves must adhere to clearances specified in NFPA 211.
Look for metal tags on the wood stove that list minimum clearances. Listed wood stoves may be installed to as little as 6 inches away from combustibles, if they incorporate heat shields and combustion design that directs heat away from the stove’s back and sides.
Unlisted stoves must be at least 36 inches away from combustibles. Ventilated or insulated wall protectors may decrease unlisted clearance from one-third to two thirds, according to NFPA 211. Always follow the stove manufacturer’s or heat-shield manufacturer’s installation instructions.
Floor Construction and Clearances
The floor of a listed wood stove must comply with the specifications on the listing (metal tag). Modern listed stoves usually sit on a 1-inch thick non-combustible floor protector that extends 18 inches beyond the stove in front.
The floor requirements for underneath a unlisted wood stove depends on the clearance between the stove and the floor, which depends on the length of its legs. Unlisted wood stoves must have floor protection underneath them unless they rest on a floor of non-combustible construction. An example of a noncombustible floor is one composed of only masonry material sitting on sand or gravel.
An approved floor protector is either one or two courses of hollow masonry material (4 inches thick) with a non-combustible quarter-inch surface of steel or other non-combustible material on top of the masonry. This floor for a non-listed wood stove must extend no less than 18 inches beyond the stove in all directions.
Vent-Connector and Chimney Clearance
Interior masonry chimneys require a 2-inch clearance from combustibles and exterior masonry chimneys require a 1-inch clearance from combustibles. All-fuel metal chimneys (insulated double-wall or triple wall) usually require a 2- inch clearance from combustibles.
Double-wall stove-pipe vent connectors require a 9-inch clearance from combustibles or a clearance listed on the product. Single wall vent connectors must be at least 18 inches from combustibles. Wall protectors may reduce this clearance up to two-thirds.
See also “Wood Stove Clearances” on page 266 and “Stove Clearances” on page 266.
All components of wood stove venting systems should be approved for use with wood stoves. Chimney sections penetrating floor, ceiling, or roof should have approved thimbles, support packages, and ventilated shields to protect nearby combustible materials from high temperatures. Perform or specify the following inspection tasks.
ü Inspect stove, vent connector, and chimney for correct clearances from combustible materials as listed on stoves and vent assemblies or as specified in NFPA 211.
ü Each wood stove must have its own dedicated flue pipe. Two wood stoves may not share a single flue.
ü If the home is tight (<0.35 ACH), the wood stove should be equipped with a dedicated outdoor combustion-air duct.
ü Inspect vent connector and chimney for leaks. Leaks should be sealed with a high temperature sealant designed for sealing wood stove vents.
ü Galvanized-steel pipe must not be used to vent wood stoves.
ü Inspect chimney and vent connector for creosote build-up, and suggest chimney cleaning if creosote build-up exists.
ü Inspect the house for soot on seldom-cleaned horizontal surfaces. If soot is present, inspect the wood stove door gasket. Seal stove air leaks or chimney air leaks with stove cement. Improve draft by extending the chimney to reduce indoor smoke emissions.
ü Inspect stack damper and/or combustion air intake damper.
ü Check catalytic converter for repair or replacement if the wood stove has one.
ü Assure that heat exchange surfaces and flue passages within the wood stove are free of accumulations of soot or debris.
ü Wood stoves installed in manufactured homes must be approved for use in manufactured homes.