Popping Noises From the Gas Furnace

Furnace Ducts

• Tim Carter, the titular builder of online home building resource Ask the Builder, and author Henri De Marne, both attribute the majority of furnace popping to ducts. Heating ducts are metal conduits that transport air into, and toxins out of, gas furnaces. Ducts bring air, necessary for combustion, into the furnace. They also remove toxins created by the burning process, such as carbon monoxide and toxic materials within the gas, from the furnace and the home.

Duct Popping

• Duct systems connecting to gas furnaces are made of metal. These ducts feed directly into the furnace, often entering the body of the unit and connecting to the area within the furnace where the gas burns. When you turn your furnace on, it generates extreme heat. This heat warms air within the heater. Warm air then travels through the ducts connecting to the furnace, which in turn significantly increases the temperature within the ducts. This increase causes the metal of the ducts to expand, resulting in a popping noise.

Gas Ports

• Problems with gas ports may also result in popping noises within your furnace. A gas furnace receives gas from numerous sources. These sources, known as ports and resembling nozzles, feed gas into the main chamber of the furnace. When you turn a furnace on, the nozzles begin spraying gas. A popping noise may occur in a nozzle when it goes into action or if one of them unexpectedly extinguishes a flame. The sudden disappearance of a flame, due to a clogged or ill-fitted gas port, can cause a popping noise. Gas port problems commonly arise if you change the type of gas your furnace runs on.

Dealing With Popping

• If your ductwork is the source of the popping noise found in your gas furnace, you can do little to change this -- short of swapping out your metal duct system for one made of PVC or some other material that doesn’t expand as it heats. To determine if duct expansion is causing the noise, listen carefully to the source of the noise when your furnace is on. If popping comes not just from the furnace but from areas around it as well, your problem probably stems from duct expansion. Fixing clogged or problematic gas ports requires turning the furnace off, disconnecting it, opening it and cleaning or replacing the ports. Contact an expert for help in this area to avoid problems such as explosions and fireballs.