Why a Furnace Makes Loud Noises
If a furnace makes a loud noise when starting up, it’s typically caused by a gas buildup from a delayed ignition.
Furnaces are complex yet essential machines in most homes. Like any machine, they can experience troubles. In our last blog, we explored why a furnace may emit a burning smell or a humming noise. This blog expands on common symptoms of furnace issues with why a furnace may emit loud noises while running and turning off. Homeowners should be familiar with these symptoms to know what to do if the issue arises.
Loud noises while running
If a furnace makes a loud noise when starting up, it’s typically caused by a gas buildup from a delayed ignition. This is a severe issue which should only be addressed by a professional. A boom noise could indicate undersized or clogged ductwork or that the burners must be cleaned and maintained.
If the furnace makes a clanging sound, it could come from the pipes. Pipes expand as they warm and contract as they cool, which can cause a clanging noise to radiate from the furnace ducts. There is usually no cause for alarm; however, if this noise is new or unusual, contact a professional for inspection.
A sudden rattling noise can be as simple as loose plates on the furnace. Tighten down the screws that hold the plates in place. If this doesn’t correct the problem, call a professional immediately. Rattling in a furnace can indicate a leak in the exchanger, which, left unchecked, could result in a carbon monoxide buildup in the home.
Rumbling coming from a furnace may be a sign the burners are dirty. This can also signal that the pilot light is too high and needs to be adjusted. Screeching, chirping, bumping, or thudding noises can all point to issues within the mechanics of a furnace. They can result from metal on metal, usually caused by a broken fan or belt, a warped plate interfering with the fan, or an internal bearing.
Loud noises while turning off
A furnace making loud noises while turning off could signify a dirty system. First, check that the filter isn’t dirty or misaligned, which impedes airflow and causes a backup. Clean or replace the air filter seasonally to stop excess dirt from building up. A loud noise while turning off could also be from a buildup in the ductwork that blocks and traps airflow. In this case, have a professional clean the ductwork thoroughly. Lastly, a fan inside the ductwork is used for heating and AC. If this fan is dirty, it could cause banging noises as it switches off; in this case, the fan needs to be cleaned.
Metal in a furnace naturally expands and contracts as the system cycles off and the temperature changes in the ductwork, which may cause loud noises. Adjust the dampers on the side of the furnace that supplies airflow to the home. Open the dampers one at a time, then test to see what difference each makes to the banging sounds. A bypass damper can help absorb vibrations that cause banging furnace noises. Add a bypass damper or recalibrate or repair the existing one.
Finally, the actuator, which works to help push the air through the system, could be misaligned. Adjust the actuator up or down until there’s a change in the banging sound. Contact a certified heat and cooling technician when in doubt, as this can be challenging.
Furnaces that emit loud noises, either while running or turning off, can be alarming. Homeowners must be familiar with these symptoms to stay calm and act appropriately. Furnaces are complex machines, so it’s usually best to contact a professional HVAC company immediately when an issue arises.
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.
