Are wood burning stoves safe?

2/1/2019 (Permalink)

The chimney for a wood burning stoves must be masonry or UL-listed, and factory built. Never, under any circumstances, should an unlined, single brick chimney be used for a wood stove. Single brick chimneys are prone to failure, which may allow potentially dangerous situations to develop.

There are lots older homes that have unlined chimneys constructed of double brick. These may be used for a wood stove after carefully checking for cracked mortar or loose or missing brick. Metal sleeves that are listed by the Underwriters Laboratory may be used as chimney lines if they were designed for such use.

Factory built, metal chimneys must never be used with a coal stove, as the corrosive flue gases produced by a coal fire will cause a rapid failure of the chimney. Metal chimneys should be completely disassembled after a chimney fire and checked for damage. Discoloration of the exterior indicates a possible breakdown of the insulating material. Any questionable section should be replaced.

A wood burning stove should never be connected to a wood stove flue which vents an oil burner. Deadly, unburned vapors from the oil burner could back up into the stove and the room where it is located.If your home came with an existing wood burning stove, you should have it serviced and inspected before use.

Venting the stove is the most important part of the wood-burning system. 90% of all stove-related fires start within the venting system. A venting system is not a chimney – it consists of lengths of 24-gauge or heavier, insulated stovepipe which connects the stove to an approved chimney.

Stovepipe clearance is extremely important. It must never pass through an interior wall, floor, or ceiling. Where possible, the insulated stovepipe must go directly into a lined masonry or UL-listed, factory-built chimney. If stovepipe must pass through an exterior wall to reach the chimney, maintain an 18-inch minimum clearance to all combustibles. Consult fire codes and use metal thimbles designed for this purpose.

Use proper fuel

Hardwoods, such as maple, beech, ash, hickory, or oak, are the best fuel for a wood burning stove. Wood should be cut, split and air dried for at least a year before burning. Well-seasoned hardwood will show cracks in the ends. Wood will dry faster and remain dry and protected from the elements if stored in a shed or under a tarp.

Regular cleaning

Use a wire brush to clean your stovepipe and chimney at least once a year. Also, occasionally use controlled high-temperature fires in the stove or furnace. Salt-based chemical cleaners are not very affective.  Never use heavy items such as chains, bricks or a brush on the end of a rope, because they could seriously damage the interior chimney lining.

Avoid creosote buildup

Creosote is a highly combustible fuel that burns intensely. A slow-burning fire such as those found in a modern, airtight stove damped way down, produces a flue temperature in the 100-200 degree Fahrenheit range. These comparatively low temperatures do not sufficiently carry all of the unburned, combustible gases into the atmosphere. Instead, they condense along the walls of the stovepipe and the chimney as creosote. Creosote may take 3 forms:

• A sticky liquid that will run down the chimney and stove pipe where it will be burned
• A flaky, black deposit which is easily removed by brushing
• A hard, glazed tar which is almost impossible to remove, except by a certified professional chimney sweep

Tips for building a fire

• Season wood outdoors through the hot, dry summer for at least 6 months before burning it. Properly seasoned wood is darker, has cracks in the end grain, and sounds hollow when smacked against another piece of wood.
• Store wood outdoors, stacked neatly off the ground with the top covered.
• Start fires with clean newspaper and dry kindling.
• Burn hot, bright fires. But use smaller fires in milder weather.
• Let the fire burn down to coals, then rake the coals toward the air inlet (and wood stove door), creating a mound. Do not spread the coals flat.
• Reload your wood stove by adding at least three pieces of wood each time, on and behind the mound of hot coals. Avoid adding one log at a time.
• Regularly remove ashes from the wood stove into a metal container with a cover, and store outdoors.