Smoking Fireplaces and Negative House Pressure Problems

Many homes have negative pressure problems—this is common when homes are tightly insulated

or in large or multi-story houses. Not enough make-up air can get in the house for all of the things that need air, like fireplaces, wood stoves, gas ranges, furnaces water heaters — and people.

Fireplaces can smoke or smell when a second fireplace is used or when a furnace kicks on. This is because the furnace or fireplace needs air for combustion, and takes it from the place of least resistance which is often a fireplace. This is a house problem—not a chimney problem.

When an exhaust fan is used in the kitchen or bath, or the furnace is used, this makes the problem worse because air is being removed from the home.  You may notice cold air drafts coming from fireplaces, fireplaces that smoke, Carbon Monoxide backup from the furnace, gas fireplace, or hot water heater, or leaky doors and windows. These are all symptoms of negative pressure in the house. Sometimes unexplained illness and flu-like symptoms can be an indication of negative house pressure.

Carbon Monoxide is a serious and widespread problem and CO detectors only measure 9 ppm over 10 minutes before the alarm goes off. This means that the household could be exposed to low levels of CO, which is known to cause permanent brain damage or illness. 

Note: All homes need a CO detector on each level! 

Smoking Fireplaces are usually caused by a lack of combustion air and a negative air pressure problem in the house. Fireplaces and stoves on lower levels of the home often perform poorly since they are in the negative pressure plane. In some cases, an induced draft system may also be needed. 

Symptoms of Negative House Pressure: 

· Poor indoor air quality

· Smoking fireplaces and wood stoves

· Unexplained illness that stops when you leave the house

· Carbon Monoxide backup from gas furnaces, water heaters, fireplaces, or stoves

· Mold and mildew in the house

· Leaking doors, windows, can lights, etc.

· Cold downdrafts in fireplaces

Fireplace Test:

· Place tissue paper, a newspaper page cut into strips, or a piece of saran wrap across the front opening of the fireplace and secure it at the top with tape.

· Open the damper

· Watch the paper—if it goes in toward the fireplace draft is good and there is no negative pressure

· If the paper goes out towards the room, a down-draft is occurring and this is an indication of negative house pressure on the floor where the fireplace is located.

· Slowly open a window in the room and watch the paper, it should reverse and go in towards the fireplace—this is positive indication that there is a negative pressure problem.

If you are experiencing any of the above issues call a professional chimney sweep or HVAC company to diagnose the problem and offer a solution. 

Solutions may include the addition of an outside air door for the fireplace or room, the installation of a draft inducer on a wood-burning stove, or the installation of a whole-house ventilator. 

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Marge Padgitt is the president of HearthMasters, Inc. in Independence, MO. She is a writer, publisher and speaker.  Contact her at margepadgitt@gmail.com.