The Causes of Gas Furnace Blow Back

When gas furnaces are not installed properly or fail to receive adequate routine maintenance, the furnace may begin to experience blowback. Blow-back, a reverse-flow of gases that can occur in internal-combustion based machines, is a dangerous furnace malfunction that can cause toxic gases containing carbon monoxide to build up in your home, posing a severe risk to your family's health.

Gas furnaces have an air-intake valve to provide combustion air to the furnace. For combustion, or lighting, of the furnace to take place, a mixture of air, fuel and heat is necessary. The combustion air taken in by your furnace must be uncontaminated by fluorine or chlorine, chemicals found in many home products. Contaminated combustion air can cause the heat exchanger system to deteriorate, resulting in a blockage that will cause blowback.

If the combustion air and fuel ratio your gas furnace is receiving is not balanced properly, blowback may occur. To determine if the air and fuel ratio is unbalanced, examine the flame on the burner. If the flame is not bright blue, the air and fuel ratio is incorrect and needs to be adjusted.

Gas furnaces have plastic pipes that vent exhaust gases outdoors. If the vent pipes are not correctly installed, multiple factors may cause gas furnace blowback. If vent pipes do not extend high enough in the air, snow or dirt can clog the pipe and push gases back into your home. Pipes near cement patios or walkways may become blocked by ice condensation that forms on the cement. Vent pipes must also be protected from strong winds, which can push the air back into the furnace as blowback and possibly contaminate combustion air.