8.9 Wood Stoves and Fireplaces
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. See the EPA’s Burn Wise website for client education materials.
Solid fueled space heaters include wood stoves, coal stoves, pellet stoves, and fireplaces. Wood, coal, and pellet fired furnace and boiler systems should be treated as vented heating systems and are not covered here.
Assess solid fuel-fired appliances to ensure safe installation prior to weatherization activities. Repair or removal is an allowed H&S measure for primary and secondary solid fuel-fired heating appliances. Replacement is allowed for primary solid fuel heating appliances but replacement is not allowed for secondary heating appliances. Repair of flues and proper installation (e.g. protection of combustibles), is required for both primary and secondary solid fuel heating appliances.
Install replacement primary heaters and/or flues according to applicable codes, standards and manufacturer’s instructions. Provide adequate combustion air.
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 rear and side panels.
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 an 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 non-combustible floor. An example of a noncombustible floor is one composed of only masonry material.
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 307
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 deposits exist.
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.
Weatherization air-sealing can present special hazards for fireplaces. If the chimney draft is poor, smoke from the fireplace may downdraft into the living space causing poor indoor air quality. The occupants of the weatherized home will likely ventilate in these situations.
However near the end of a wood fire, glowing coals will remain in the fireplace. The coals radiate heat, but the top of the chimney will cool off, reducing chimney draft and lowering the available oxygen for the smoldering coals. The reduced oxygen causes carbon monoxide production without the smoke that typically encourages the occupants to ventilate.
This is a dangerous situation. Since the chimney draft is reduced the CO enters the living space instead of escaping up through the chimney. CO exposure causes drowsiness of occupants, and sometimes worse. For this reason it is extremely important to make sure there is a CO alarm installed in this combustion zone and occupants are educated to the danger signs and what to do if the alarm goes off.
Inspection and Evaluation:
• Inspect the fireplace venting and chimney, and the overall installation to ensure it adheres to the applicable code: NFPA 211 or other as determined by the authority having jurisdiction. Appliances should be inspected pre- and post-weatherization.
• Conduct pre- and post- weatherization worst case CAZ depressurization testing in spaces that have a fireplace. Since there is no consensus method for verifying safe operation of fireplaces, Grantees can propose testing policies and limits (e.g., one Grantee uses a depressurization limit of -5 in the CAZ of any wood-burning combustion appliances, including fireplaces). If the Grantee does not propose a policy and fireplaces are left operational, the vent must meet code or the home cannot be weatherized.
• To simulate the affects of an operating fireplace on other combustion appliances set a blower-door in depressurization mode to run at 300 CFM.