How To Diagnose Furnace Banging Noises

Posted on: 28 April 2018


Gas furnaces are prone to making some natural noises, such as knocking, which occurs when metal parts expand after the furnace starts. However, if you hear a louder banging or popping sound, and the noise gets more frequent, it could be a sign of a problem. Some problems may need professional service, and others you can fix yourself,  but you should investigate the cause immediately by following these troubleshooting tips.

Test for a Delayed Ignition

Noises that appear to be coming from the furnace several seconds it starts or clicking noises could be delayed ignition. It means the gas valve delays sending the gas to the burners. A clicking noise indicates the furnace cannot successfully light the burners, and booms or bangs could be the gas exploding inside the burners. 

Get an assistant to raise the temperature while you stand five feet from the furnace. Watch the burners to determine whether they light immediately. If they don't light immediately, and you hear clicking noises, clean the burners, and check the gas supply. Otherwise, contact a furnace repair professional

Clean or Replace Filters 

If a delayed ignition isn't the problem, check for a dirty fan and ductwork, which causes uneven air pressure. Air filters are commonly located in the blower department or the plenum next to the burners, and they should remove by hand. 

Soak filters in soapy water, rinse, and dry them. Replace damaged filters, and add a non-pleated filter inside the ductwork to reduce noise further. 

Adjust the Damper and Fan

Every furnace has a fan installed in the blower compartment that blows air into the ductwork with blades Sometimes, the blades get bent or loosen, which calls for fan replacement.

Locate the duct dampers, the devices that direct air, on the supply side of the ductwork. If the ductwork has too many closed dampers, it could cause the banging sound.

Turn the level one time until it hits "open" or until it comes parallel with the duct, listening for changes in noise. Also, adjust the actuator, the mechanism that pushes air through the system, inside the dampers.

Adjust and the Clean Ductwork

Ductwork can press against lumber installed near it, which is caused by expansion. To stop the noise, insert a foam pad between the frame and ductwork.

Ductwork expands and contracts with the heating cycle, which causes banging or booming. Sometimes, the ductwork may be too small for your system, but if replacing it is not immediately possible, wrapping insulation around the ducts may help reduce the noise. If you'd like to learn more, contact a company like West County Heating and Cooling.