Why Does My Wood Burning Stove Smoke Up the House?

Wood burning stoves require regular maintenance for peak performance.

Smoking is one of the most common problems of wood stoves. A poorly functioning wood burning stove, spewing smoke into your home, can damage the paint, deposit soot on furnishings and be a serious fire hazard. There are several reasons for this unpleasant problem, and you should have your chimney and stove evaluated by a professional. Resolution of the problem may be fairly simple in the hands of an expert.

Closed Damper and Improper Wood Burning

The correct size of dry wood is important for a good fire.

The damper inside a wood stove or pipe restricts the flow of smoke out. It should be fully open when stove is lit to allow maximum draft. Even partially closed, it will smoke. Shutting down air controls on the stove starves the fire of oxygen, causing it to burn poorly and smoke. Very dry wood split in small pieces and kiln-dried wooden blocks burn too rapidly, creating excess gas and smoke.

Chimney Built on Home Exterior

A wood stove needs a chimney that's the proper height for effective operation.

A chimney operates properly when the flue is warmer than the air outside the house. Chimneys built on the exterior rather than through the center become cold and are likely to smoke.

Cold Flue at Fire Start-up

Older chimneys may need repairs as bricks collapse, blocking the flue.

Once the flue warms up, the smoke will be drawn up the chimney, but by then you may already have a house full of smoke. Prime the flue before starting the fire by lighting a roll of paper and holding it in the firebox, near the flue collar (the stove opening connecting to the pipe). Burn one or two rolls to start warm gases going up flue, then light the wood fire.

Inadequate Chimney Height

A chimney cap redirects wind and keeps out debris.

A chimney should be at least three feet higher than the highest point where it passes through the roofline and at least two feet higher than any part of the house that is within 10 feet of it. An extension of the chimney or stove pipe may be needed.

Chimney Blockage or No Chimney Cap

The stacking effect works to make the house draw drafts in and out like a smokestack.

There may be creosote buildup, leaves, debris, bird nests or a partial collapse of the chimney lining or brickwork blocking the flue. This can be eliminated with regular cleaning and a chimney cap that fits on top of the chimney, deflecting wind. Caps with downdraft deflectors stop winds from blowing cold air down the flue, forcing smoke into the house.

Incorrect Size Chimney Flue and Multiple Appliances Connected to the Same Flue

This chimney cap will not deflect wind nor stop back-puffing from a wood stove.

An oversize flue requires more heat to keep it warm, affects burning and causes creosote buildup and smoking. Newer stoves, especially catalytic models, are very draft sensitive, and the oversize flue becomes a big problem. An undersize flue causes smoke to bottleneck, backing up into the house and presenting a fire hazard. The correct size of flue for your stove model should be installed. A wood stove connected to a chimney that serves a fireplace, furnace or other appliance may smoke. New standards require wood stoves to have their own flue.

Depressurized House

Extending chimney height may be necessary to stop smoking by a wood stove.

Air movement within the house interferes with chimney function. The “stack effect” causes the entire house to act like a chimney stack, drawing air up or down. Open windows, a poorly insulated roof, drafty attic or tall stairwell suck warm air up and out the chimney, drawing cold air in and blowing smoke into the house.

References

• Woodheat: All about Chimneys
• Chimney Sweepers: Wood Stove Problems
• Chimneys: Burning Secrets-Woodstove Problems