Chimney Draft Issues and Solutions
Symptom: Fireplace smokes or smells.
Problem: Smoking can be the result of a chimney flue that is dirty. Soot and creosote have built up on the walls of the flue effectively shrinking the flue size so that it is no longer is big enough to vent properly. Smell is usually associated with a very dirty smoke chamber, or ash pit. If the ash pit is getting wet from water it can smell really bad as it builds up mold in the ash. Also check for live or dead animals, animal nests and / or feces.
Solution: If the flue is just dirty, have the flue professionally cleaned and the smoking will stop. For smells chemical treatments and / or glaze chains may also be necessary to remove creosote. Remove all of the ash from the ash pit and bleach the pit if necessary. Remove any live or dead animals, nesting, and / or feces and disinfect the area with bleach (always use disposable gloves and a respirator to avoid parasite infections.) Make sure the chimney has one properly sized cap that keeps water out of the flues and off the crown. Water can also come from other sources such as through the foundation (run rain gutter spouts at least 3’ away from foundation and / or dig out and damp proof the foundation with tar and / or install a dry well), faulty flashing (replace flashing), porous bricks (breathable waterproof brickwork), damaged crown (replace crown with new concrete), masonry cracks or deterioration (re-point or rebuild masonry) and flue tiles that terminate below crown (lengthen tiles to at least 2” above crown).
Symptom: Fireplace smokes upon start-up on cold days.
Problem: Flue lining is cold and won’t draw. (Usually side of the house chimneys)
Solution: Warm up the flue by opening the damper which will let warm room air into the flue then burn some newspaper behind the damper frame start your fire burning as soon as the newspaper is burned up. A top mounted damper will help to solve this problem by keeping the flue lining warm constantly.
Symptom: After awhile of burning the fireplace smokes constantly. Exterior doors may make a “wooshing” sound when opened after the fire has been going awhile.
Problem: Building is very air tight, the fire has used up all the make-up air which causes a negative pressure in the building. (Kitchen and bathroom exhaust fans also heating appliances such as furnaces, water-heaters, pellet and wood-stoves all use up make-up air and can cause a negative pressure.)
Solution: Open a window on the windward side of the home (smoking will stop almost immediately if this is the problem) also shut off exhaust fans in bathrooms or kitchen or for a better solution have a professional install an air supply ventilator on the windward side of the home near the fireplace or preferably on the lowest floor. The best solution is for outside air intake lines on all appliances and fireplaces if possible.
Symptom: Fireplace always smokes and has since construction.
Problem: Chimney flue is not built to the 1/10th rule. Area of the flue must be 1/10th the area of the fireplace opening A=LxW (1/12th for round flues and 1/8th for rectangle flues with a high aspect ratio). Chimney could also not be built tall enough, in which case see the appropriate symptom / solution below for correction.
Solution: Have a professional measure fireplace opening area and either install a smoke guard or glass doors in the fireplace opening or an Exhausto chimney fan at the top of the chimney with an air supply ventilator on the windward side of the home near the fireplace or preferably on the lowest floor.
Symptom: Fireplace smokes occasionally, especially on windy days.
Problem: Wind induced down drafts.
Solution: Have a professional install a Wind-beater style cap.
Symptom: Fireplace smokes most or all of the time.
Problem: Chimney is not tall enough to meet code required height. The chimney must be a min of 3’ tall on all sides above the roof and then 2’ above any structure within 10’. Sometimes this still isn’t tall enough if other structures or vegetation surround the building on several sides if this is the case see the appropriate symptom below for correction.
Solution: Have a professional build the chimney 2’-3’ taller than any structures or vegetation surrounding the building or install an Exhausto fan at the top of the chimney with an air supply ventilator on the windward side of the home near the fireplace or preferably on the lowest floor.
Symptom: Fireplace smokes most of the time.
Problem: The air current over the chimney is deflected by a tall tree, an addition on the building or a neighboring building.
Solution: First, try a Wind-beater style cap. Then, if that doesn’t work try building the chimney 2’-3’ taller than any structure or vegetation that might be causing the air deflection, or if that is not possible install an Exhausto fan at the top of the chimney with an air supply ventilator on the windward side of the home near the fireplace or preferably on the lowest floor.
Symptom: In a building with multiple fireplaces, when having a fire in one room, smoke comes out another fireplace that isn’t being used.
Problem: If there is a chimney cap it could be emphasizing a pressure problem which is causing smoke to be suctioned down another flue (this can also happen without a cap installed on the chimney). Usually the building is very air tight, and the fire or appliance has used up all the make-up air which causes the other chimney to become an air intake duct.
Solution: Have a professional install top mount dampers in each flue, or install a solid sheet metal divider in the chimney cap between the flues. However, it is better to address the pressure problem and install an air supply ventilator on the windward side of the home near the problem fireplace or preferably on the lowest floor. (Or even better, install an outside air intake line on all appliances and fireplaces if possible.)
Symptom: Smoke is not exiting the top of the chimney efficiently, and is going down another flue, or is backing up in the flue that is venting.
Problem: The chimney cap may not be tall enough and / or the flue tile may be to close to the bottom of the cap lid. Or it could be that the cap is causing the airflow above the chimney to be deflected improperly.
Solution: Check to see that the area of the screen and / or the area between the top of the flue tile and the bottom of the cap lid is 3x the size of the flue area, if it is not install a cap with the larger and properly sized screen height. Or if the cap is deflecting the airflow remove the cap and install a mesh “roof vent guard” style cap.
Symptom: Smoke is coming out of a wood stove in intermittent puffs.
Problem: Back puffing (caused by improper wood and / or burning / loading techniques).
Solution: Wood is to dry. Or, stove is overloaded with wood. Or, not enough air is being supplied to the stove (open up the intake damper).
Symptom: Furnace or boiler flue builds up debris in cleanout. Or poisonous flue gases are entering living area.
Problem: Chimney lining is deteriorated or there is no lining, which causes the chimney to leak and not have proper draft. (Chimney lining problems are the most common cause of this problem.) Or the chimney is not tall enough to meet code required height. The chimney must be a min of 3’ tall on all sides above the roof and then 2’ above any structure within 10’ (as long as your chimney meets the minimum standard, usually height is not the issue with furnaces and boilers because the temperature difference in the heating season between inside and outside increases draft effect, also hot flue gases naturally rise, so they easily go up the chimney and vent to the outside.) Or it may be that the home is very air tight so the furnace or boiler is using up all available make up air, which will cause the chimney to work poorly or not at all.
Solution: Install a new lining in chimney and new breeching pipes to appliances (make the breeching as steep an angle as possible also as short as possible) be sure to take out any unnecessary elbows, lengths or tees in the exhaust piping while maintaining a rise of at least ¼” over every 12”. Make sure the chimney meets the minimum required height. If deemed necessary have a professional build the chimney 2’-3’ taller than any structures or vegetation surrounding the building. Sometimes this still isn’t tall enough if other structures or vegetation surround the building on several sides. If this is the case, you must continue to build the chimney higher until you reach the area of low pressure above the house. If that is not possible mechanical draft inducers can be installed by a professional furnace / boiler technician, but only if there is already a liner and it is in good shape, otherwise a new liner is absolutely necessary when using mechanical draft as poisonous gases can be forced into the home through the walls of the chimney and structure. If the problem is from lack of make up air, install a outside air intake directly to the appliance (if that’s not possible use a passive system such as or an air supply ventilator mounted on the windward side of the home preferably on the lowest level or a mechanical “fan in a can” in the room with the furnace).
Call the main office for an appointment at (781) 233-2321
Serving all of eastern MA. and southeastern NH.
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