Smoking Chimney

Sometimes you need to call a professional… and sometimes you don’t. Here are a number of tips to help resolve common problems with chimneys.

Constant smoking problems

Constant smoking problems are often the easiest to diagnose while being the hardest to correct. Many constant smoking problems are the result of improper construction or design and may require extensive modification of the chimney system to correct. Below is a description of the common design problems which may lead to smoking problems.

Damper is Closed

Check to see if the damper is open or functioning properly. More people overlook this than you might think!

Inadequate Air Supply

Open a window or door as close to the fireplace as possible. If the smoking lessons or stops when the door or window is open, the problem is inadequate air supply. Homes today are designed to be as air tight as possible. The flow of air up the chimney cannot exceed the flow of air into the house. All air removed from the room during the burning process must be replaced by fresh outside air. This air would normally enter the house through small cracks in the doors and windows.

Many fireplaces being installed in apartments now come with an “outside air source”. A lever or handle will usually be found in or near the fireplace. This can be opened to allow fresh air into the firebox to replace the room air being used. If your fireplace does not have an outside air source one can be installed in masonry fireplaces.

Fireplace Opening is too Large

This problem typically allows the fire to burn comfortably for a while, but the room will become smoky after a time. The fireplace opening should be sized based upon a relationship with the chimney flue. An ideal fireplace opening would be no more than ten times the cross sectional area of the chimney flue. For example if the inside dimensions of the flue are 10 x 10 equalling 100 square inches, then the fireplace opening should not exceed 10 times this or 1000 square inches.

If a fireplace opening is to large it will allow more air into the fireplace than the flue can exhaust. Fortunately, this is an easy problem to fix. By installing a fireproof shield at the top of the fireplace opening, the effective opening can be reduced. Glass doors could also be used.

The Chimney Flue is Obstructed

Extinguish the fire and look for obstructions. Birds nests are commonly found in chimneys and may often be large enough to restrict flow. Soot and creosote can plug or restrict the airflow of others. If the chimney is older, fallen brick or mortar may be obstructing the flue. Any obstructions must be removed. A blocked chimney is a fire hazard and should never be used until completely cleaned and inspected. Chimneys blocked as a result of structural failure should be condemned and rebuilt.

Improper Construction or Design

It is possible that a masonry chimney was poorly designed. If your fireplace consistently smokes and none of the ideas presented above work, It may be that your chimney has design flaws. Please contact our office about this.

Occasional smoking problems

Occasional smoking problems are often the most difficult to diagnose , but most are simple to correct, if the problem can be tracked down! A brief description of the most common occasional smoking problems follows. With experimentation and patience we can discover the problem and you may at last enjoy the fire you long to!


If the temperature outside is fairly close to the inside temperature and their is a high pressure cell in the area, you probably do not have enough air pressure in the house to maintain a draft. The only solution here is to wait for the weather to change.

Competing Vents from other Appliances

Check for the existence of competing vents. Kitchen and bathroom fans, or chimneys for other fireplaces or stoves may overpower your chimneys draft by drawing the air they need through the “smoking” chimney. This problem can be solved by ensuring each vent has adequate air flow. If the house is two or more stories, hot air rising and escaping from the top story can reduce the air pressure of the ground floor, and pull air in from the outside, even down the chimney.

Wood Supply

Check your wood. Excess moisture in the wood can be one problem. Dense woods which are hard to light can cause an initially cool fire which can result in poor draft and excessive smoke.

Chimney Height

Measure the effective height of your chimney. This includes only the part of the chimney that is above the point the woodstove is vented into the chimney or the point above the firebox of a fireplace. Any chimney with an effective height of less then 10 feet will generally cause problems. The chimney or flue pipe must extend out of the top of the roof 3 feet as well as being 2 feet higher than anything within 10 feet.

Chimney Caps

Check for obstructions that might form as downdraft. Roof lines, trees, hills, or nearby structures can all cause downdraft problems. When the wind blows over and down around them, the downdraft simply blows down the flue, sending the smoke into the house. A chimney cap will reduce the effects of those rear vertical blasts of wind.

Other Types of Smoking Problems

Unused Fireplace Smokes while Another is being Used

Often a fireplace will smoke while another in the house is being used due to the “inadequate air flow” idea presented above. This problem can at times be easily solved by raising the flue height of the offending fireplace 6-12 inches. This is an inexpensive job when performed by our company and will in most cases solve the problem.

Smoking When Stove or Glass Doors are Opened

This is most often cured by opening the doors slowly, allowing for the air flow to adjust in the firebox. Opening the draft fully several minuets before opening the doors will raise the temperature and eliminate a lot of the smoke.

Smoking Problems when Household Doors are Opened

A door opened or closed rapidly can result in a change in your homes air pressure, causing the draft to briefly stop or even reverse. An outside air source would solve this type of problem.

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