Fireplace External Air Supply

The additional air to feed the fire must come from somewhere.

Fireplace external air supply.

External air intakes are used to bolster a fireplace s supply of air. In those homes the fireplace would not be able to draw in enough new air through cracks and vents causing incomplete combustion underpressure and other undesirable outcomes. The fireplace installer technician mentioned the possibility of adding an external air supply to the wood stove. When the fireplace runs out of air it begins to create vacuums and usually smoke ends up pouring back into the house.

Fireplaces especially wood burning fireplaces can consume a large amount of oxygen in a short amount of time and the normal vents traditionally installed are not always enough to supply the needed oxygen. In other words you need to be able to close off the exterior air supply and it must be configured to prevent burning material think coals popping off a burning log from entering the supply duct. He advised against it though because in his experience this is only necessary for very new highly insulated homes. This air duct is supplied at the top by an air exhaust chimney.

The manufacturer of fireplace inserts and stoves have responded to this new challenge. Modern wood heaters can be connected to an external air duct to secure the necessary combustion air. In addition to the chemical reactions between the fuel and the air there is expansion due to heat which pushes gases up the exhaust and draws in a correspondingly larger volume of air. A fireplace consumes vast amounts of air each minute as the fuel burns.

In a sealed fireplace with combustion air supply this isn t an issue. The fresh air vent in the hearth may be blocked or it may not be able to supply enough air to satisfy the appetite of the fire. For masonry fireplaces the area of the exterior air passageway must be at least 6 square inches but not more than 55 square inches. However my particular problem is with a wood fired oven.

Since the air consumption of a wood stove is so low the risk of reversal of a ducted combustion air supply outweighs any advantage gained by bringing air from outdoors. The chimney cap buying guide and the chimney pipe buying guide will help you find out what your options are and how. It can easily be 250 to 350 cubic feet of air per minute. Proper research prior to installation is the key to simplifying the process.