Why Does the Furnace Make a Loud Noise When It Turns Off?

Mar 5

A loud noise coming from the furnace when it turns off could be caused by something very simple. The noise may be described as a loud boom or bang and can be disconcerting, especially when it first happens.

Below are some reasons a banging sound may be heard and how to fix these loud banging noises coming from the furnace.

Replacing a Dirty Filter

A very simple reason for hearing a banging sound when the furnace turns off is due to the inside filter. If the filter is dirty or not placed correctly, air may not get out properly, causing a backup. Once the furnace cycles off, a loud banging noise is heard as the metal in the furnace expands due to the excess air. Clean or replace the filter often to prevent excess dirt buildup. If this does not help, consider other causes.

Cleaning the Ductwork

Buildup in the ductwork may also cause banging noises. This buildup is similar to the buildup in the air filter in that it causes air to flow incorrectly and become trapped. Having a professional clean the ductwork thoroughly can reduce or eliminate loud noises.

Adjusting the Dampers

The loud noises could be caused by the natural expansion and contraction that happens as the system cycles on and off, caused by temperature changes inside the ductwork. If this is the case, adjusting the dampers on the side that supplies airflow to the home to an open position can help with the noises. Open the dampers one at a time and test to see what difference it makes to the banging sounds.

Adjusting the Actuator

Adjusting the actuator in the system can sometimes eliminate noises coming from the furnace. An actuator helps push the air through the system. Adjust the actuator up or down until there's a change in the banging sound.

Cleaning the Fan

Another cause of noises coming from the furnace could be the fan that is used for both AC and heating and is found inside the ductwork. If this fan is dirty, it could easily be causing banging noises as it switches off. Cleaning this fan may remedy the loud noises.

Forecast Heating, Cooling, and Refrigeration serves residential and commercial customers in Summerlin, Anthem, North Las Vegas, Boulder City and Las Vegas. Call us at 702-919-4546.

Furnace Problems