How to Check an LP Furnace Combustion

LP Furnace Combustion

• The combustion process in an LP furnace relies on the proper mix of air and gas to burn at optimal efficiency levels. Checking a furnace’s combustion levels also allows homeowners to determine whether any safety issues exist concerning leaking combustion gases. Ideally, LP gas combustion processes produce minimal residues on furnace component surfaces, such as burners, ignition switch and heat exchanger wall surfaces. In effect, any by-products or exhaust fumes produced should flow up and out the chimney flue into the outside air.

Flue Gas Spill Switch

• A flue gas spill switch sits on top of the draft hood of an LP furnace’s heat exchanger compartment. The spill switch acts as a safety device that measures the amount of combustion gases that escape from the chimney flue during combustion processes. An excess amount of combustion gases may indicate carbon monoxide gases are leaking into a home’s living spaces. When gas leaks occur, the switch becomes increasingly warm to the touch. The switch also has an automatic shutoff device that shuts down the gas burner when high levels of combustion gas seep through.

Carbon Monoxide Gases

• An LP furnace combustion analysis involves using a measurement or analyzer device -- known as a combustion check meter -- to measure air and gas level mixtures within a furnace’s combustion process. According to the Contracting Business reference site, carbon monoxide (CO) levels should stay within certain safety ranges when performing a combustion gas check on a furnace. CO levels should go no higher than 100 parts per million (ppm) in terms of CO amounts versus air amounts. During furnace operation, CO levels should remain between 0 and 99 ppm.

Oxygen Gases

• In order for LP gas combustion to occur at optimal rates, a certain level of oxygen gases must be present within the combustion chamber. While performing a combustion process check, oxygen levels should remain between 6 and 9 percent on a consistent basis. Furnace manufacturers may set oxygen combustion rates at higher levels so the furnace operates at higher efficiency rates. To ensure carbon monoxide levels remain within safe ranges, oxygen levels should be re-adjusted to the 6 to 9 percent level, according to the Contracting Business reference site.