The everyday operation of a furnace has a sound all its own, an almost comforting rumble as the unit works to make your home a more cozy place. However, some furnace noises are not so comforting. Some indicate damage and others warn of danger. Knowing the difference between normal operational sounds and warning bells is an important part of keeping you and your family safe.
Common Furnace Noises
Standard furnace operation is typically performed to the tune of low clicking or humming sounds, especially as the furnace kicks on. It’s when the sounds start to deviate that your ears should perk up. Getting to the root of unusual furnace noises is the first step to keeping your home a safe place.
Humming
Humming is a common operational sound for furnaces. However, if the sound becomes noticeably loud, it may be indicative of a problem with your capacitor or blower fan.
Clicking
Clicking is a common sound when a furnace first boots up. However, when those furnace noises persist through the heating cycle, they may indicate a problem with the ignition system. Clicking may be the result of your furnace trying and failing to perform normal ignition steps. If your furnace keeps clicking, check for a defective ignition board or valve, damaged flame sensors, or dirty burners.
If the clicking comes from outside of the furnace, it may suggest a problem with the compressor, control panel, or fan motor. A furnace technician can help you get to the root of the problem.
Popping
Sometimes popping sounds in the furnace are the result of ordinary operation. They are the result of your system’s ducts expanding and contracting with the change in temperature. That being said, these furnace noises should not be loud enough to startle you. If the popping is noticeably loud, it may indicate that something has gone wrong in the ducts. Check to make sure your ductwork is intact.
Popping may also signal a problem with the ignition system, particularly dirty burners. This is common when a house settles and allows sediment to collect on the burners. Despite its normality, issues with the burners can lead to cracking the heat exchanger—and deadly carbon monoxide poisoning. Avoid the risk by cleaning your furnace’s burners every year.
Banging
If your furnace is making an obvious banging noise, the problem may be caused by a small gas explosion, the result of a delay in ignition. When the gas burners in your furnace don’t ignite on time, that gas builds up and can even leak into the rest of your home. Burner failure may be caused by a clog or other pressure issue. Leave such repairs to the professionals to avoid dangerous gas leaks.
Rattling
A rattling furnace noise can result if something in your furnace is loose. The rattling is indicative of the vibrations caused by loose components in the what exchanger, blower motor, gas burner, or igniter. An HVAC professional can often tighten up loose parts. If the only loose parts are panels or the furnace door, you can likely tighten them up on your own.
Scraping
Of all the furnace noises on this list, scraping is certainly the most grating. Scraping sounds like metal rubbing against metal because that is what is happening. If the ball bearings or the blower wheel in your furnace are loose, your furnace may let you know with a scraping sound. In such an event, the blower wheel may need to be replaced.
Rumbling
Furnaces sometimes produce a rumbling sound at the end of the cycle. This slightly unsettling sound, like so many we’ve discussed, may indicate an issue with the burner. When fuel continues to burn in the combustion chamber when the burners are not in operation, the result is often a low rumble. Don’t leave this (or any) furnace noises unresolved. Reach out for a professional’s opinion.
Shrieking
A high-pitched squealing or shrieking noise is a sure sign your furnace has a damaged belt. To avoid further damage and to keep your household safe, the belt will need to be replaced posthaste.
Whistling
A whistling furnace likely indicates clogged air filters. This furnace noise can usually be cleared up with relative ease by replacing the filter. Alternatively, whistling may indicate limited air flow due to blower motor problems.
Silent Furnace Problems
While strange furnace noises can be unsettling, the worst furnace problems may not make any sound at all. For example, a carbon monoxide leak can be a silent but deadly furnace problem. The colorless, tasteless, and odorless gas can cause nausea, dizziness, fainting, and even death when inhaled. Prevent gas leaks in your home by making sure your furnace maintenance is up-to-date.
