Troubleshoot Fireplace Backdrafts/Downdrafts

Inside your home, the fireplace is often competing with central heating systems, ceiling fans, exhaust fans, and other fuel-burning appliances for oxygen continuously flowing in and out of the house. A disruption in the airflow or a sudden change in air pressure can create drafting issues, including backdrafts and downdrafts.  When a backdraft/downdraft occurs, smoke, soot, and dangerous fumes are forced down the chimney and out of the fireplace. It can cause the house to fill with smoke covering nearby flooring and furnishings with ash and soot. Here are a few tips for troubleshooting your fireplace for backdrafts/downdrafts.

Flue Obstruction

Flue obstructions are common, mostly if you don’t regularly sweep the chimney. The build-up of creosote, soot, and other debris can gradually restrict the airflow inhibiting the venting of smoke and exhaust. Small animals like birds, raccoons, and squirrels can enter an open flue through a damaged or non-existent chimney cap and cause an obstruction. Leaves and twigs from nearby trees can clog the flue pipe. When the rising hot air can’t escape the flue due to a blockage, the negative air pressure creates a backdraft causing the exhaust and gases to blow back into your living space. Clearing the flue obstruction will restore the airflow to the chimney and help avoid a backdraft.

Negative Air Pressure

When a chimney is venting correctly, the air pressure is neutral as the rising warm air and exhaust that vents out the flue are simultaneously replaced with cooler outside air being pulled into the fireplace. It’s this constant flow of oxygen that keeps the fire burning in the fireplace. If there is an obstruction in the venting that interrupts the airflow, negative pressure builds in the flue, causing a backdraft forcing the smoke and fumes back down into the living space. Negative pressure can occur when there is a flue obstruction or insufficient air is being drawn into the fireplace. It is common in energy-efficient homes with airtight home envelopes. Opening a window or installing an external intake vent can help relieve the negative air pressure.

Cold Chimney

Starting a fire in a cold chimney can also create a backdraft. As the fireplace draws in the oxygen to feed the fire, the lighter cooler air isn’t sufficiently warm to push the heavier hot air and smoke up the flue. Instead, the smoke and fumes exit the fireplace.  Insulating the chimney chase – all the way to the chimney chase top can help alleviate a cold chimney, particularly if you have an exterior masonry chimney. Another option is to warm the flue before lighting the fire. To warm the flue, light some rolled-up newspaper and hold it under the flue inside the firebox. When the flue is warmed up, you should feel the draft reverse the airflow and go up the chimney.

Unseasoned Wood

Burning wood in the fireplace with a high moisture content may not be hot enough to create the necessary draft in the chimney to push the smoke up the flue, causing a backdraft. It is recommended to burn wood that has been seasoned or dried for at least six months or longer.  Ideally, the moisture content should be below 20%. Seasoned wood burns hotter and more thoroughly with less smoke and creosote. Fresh or green wood typically has a 60% moisture content and should be avoided.

If you’re experiencing drafting issues or other chimney problems, the experts at Chimney Saver Solutions can solve your chimney backdraft/downdraft issues.