Beyond the typical drone of a central heating system, there are other strange and inevitably worrisome noises that can emanate from your furnace. If you’ve ever been jolted awake by a banging noise, startled from a Netflix binge by a squealing sound, or just generally found yourself scratching your head at whatever racket is coming from the garage or utility closet, then this is for you!
Here are some common sounds that your furnace can make, what they may mean, and which should send you immediately to your HVAC contractor.
Much like the whistling of a teakettle, a whistling sound coming from your furnace can mean that air is escaping. It’s typically harmless, but that doesn’t mean it won’t cause you headaches.
Whistling could come from leaks in your ducts as air escapes, which, while not harmful in itself, can lead to system failure over time. It also means warm air is escaping into the attic or walls and not actually warming your home, which will cost you in increased energy bills. Plus, if your ducts are that old and leaky, it’ll be as easy for insects and critters to get in as it is for air to get out.
Whistling could also be a sign of a clogged filter or obstructed vent, so check both as your first line of defense. If tightening a vent cover, moving a file cabinet, or changing a filter doesn’t do the trick, then ask your HVAC contractor to check for duct leaks.
Finally, whistling from a gas furnace can come from a faulty gas valve, which allows gas to escape at high pressure. If you smell gas along with that sound, turn the system off immediately and call a service technician.
You don’t have a ghost in the machine, but you could have bigger problems. At its worst, rattling can indicate a cracked heat exchanger, which will allow carbon monoxide into the house, creating a dangerous environment for you and your family.
Before you panic, though, check for a more common culprit: loose screws or panels. Follow the source of the sound to see if a bit of tightening solves the problem.
Rattling can also come from the motor or fan, which usually means imminent failure, so you should call your HVAC pro as soon as possible.
And finally, if you hear rattling from the walls or somewhere other than your furnace, it could be coming from loose or improperly sized ducts. Again, while not specifically a danger, it means you’re probably losing heat – and money.
In an otherwise functioning furnace, a not-too-loud-but-probably-irksome hum can simply mean you have a loud transformer. This kind of hum is only problematic insofar as it’s annoying. Sometimes you can reduce the hum by tightening its bolts.
If it’s especially loud, or seems to be getting worse, the transformer may be failing and you should call a technician sooner rather than later.
Humming can also come from the motor or the fan. If that’s the case, both mean a part is in danger of failing so you should definitely get a pro on the case before you’re left out in the cold.
A scraping sound of the metal-on-metal variety is usually a sign that you’ll need a repair technician, and it’s distinctive (and annoying) enough that you’ll recognize it pretty quickly. Generally, it means there’s a fault in your blower wheel and it can range anywhere from a simple fix like tightening a part, to requiring an immediate replacement.
Sometimes a blower wheel comes loose in its housing. Left to its own devices, it can bang against the housing and cause damage. You may also hear a squealing or scratching sound as the wheel scrapes against the housing.
Whatever the case, if you hear a scraping noise you should turn the system off and call for assistance before it gets worse.
This is another “you’ll know it when you hear it” sound. Much like the squealing sound your car makes when a belt goes, your furnace can make a similar sound when its belt is loose, damaged or frayed. Squealing can also be a sign of poor lubrication, so save your furnace (and your ears) and turn the system off until the problem can be resolved.
The belt may simply need tightening, or it may need to be oiled properly. If it’s damaged, it will have to be replaced, just be sure to turn the system off immediately to prevent additional harm.
What’s the difference between a scrape, squeal and screech? Sometimes not much in terms of sound, but they can mean very different things when it comes to the ailments of your furnace.
Consider how distinctive the sound is – metal-on-metal scraping is a fairly unique sound, as is the more high-pitched squeal associated with a damaged belt. But sometimes it’s a little more… well, screechy. In that case, it could be either. Your blower may be loose and scraping its housing, or a fan may be starting to go.
Another possibility is a problem with the motor bearings, which can also come down to a problem with the motor or lubrication. Any sound of this nature is a good indication that you should shut the system down and call a technician to address the problem before other parts get damaged, too.
One of the most common causes of clicking sounds is a problem with the ignition system. If the gas valve is broken or clogged, it will fail to let gas out. As a result, the ignitor will keep trying to light the pilot and will make a clicking sound not unlike the one you hear trying to ignite an empty lighter.
If you hear clicking and aren’t getting heat, that’s most likely the culprit.
The flame sensor can also be damaged or dirty, which means it won’t send the proper “lit” signal and the ignitor will keep clicking.
If the clicking sound is happening while your furnace is running, it could mean a cracked heat exchanger. The clicking happens as the metal heats and expands. Like we mentioned before, a cracked heat exchanger can mean carbon monoxide is leaking into your home, a dangerous or even deadly problem.
It’s a good idea to keep a carbon monoxide detector in your home, and to shut your furnace down and call an HVAC technician if you hear this potentially dangerous sound.
There are bangs and then there are BANGS. If you hear a low-ish bang when your furnace starts up, especially if it’s fairly new, it could simply be the expansion and contraction of the metal and ductwork. If it’s not terribly obtrusive and doesn’t get any worse, this is most likely just its normal operation.
It could also indicate flimsy ductwork or airflow issues (remember those vents you closed to try to divert heat to colder rooms? We’ve warned about that!)
But if the bang is loud, it could be a dirty burner causing a delay in ignition. If ignition is delayed, gas can build up and cause a mini-explosion when it finally lights. A bang of this nature is obviously quite a bit more dangerous and warrants an immediate call to your HVAC technician.
If you smell gas, if your system is older, or if the sound repeats or worsens, then don’t delay in getting a professional to check it out.
Popping is the less worrisome cousin of banging. It’s one of the more harmless sounds on the list and is usually a result of air ducts expanding and contracting. When your system kicks on, the temperature change creates a change in air pressure that can cause this popping sound.
You may also hear slight popping noises as the system cycles down, for the very same reasons.
Popping plus whistling is usually a sign that your ducts are either thin, leaky, dirty or perhaps not properly sized.
Just be mindful of when a pop turns into a bang. When in doubt, get a pro’s opinion.
You know the sound that playing cards make when you shuffle them (or if you’re old enough to remember, when you clipped them to the spokes of your bike tires?)
Much like cards smacking against spokes, this sound probably means something is smacking against the blower blades. This isn’t the worst sound but it could lead to bigger issues if left unaddressed. If whatever is stuck comes loose, it could hit the housing causing more damage. Even if it never moves, it could cause your motor to wear out a lot faster. It’s best to find the source of the problem and correct it before a crisis.
Strange and unidentified sounds coming from your furnace should never be ignored. Sometimes they require simple fixes that will prevent bigger problems in the long run. And sometimes they’re a matter of your safety – and even your life.
If you’re not sure what the sound is that’s coming from your furnace, get in touch and we’ll visit your home to take a look. We’re available for emergency repairs as well as for ongoing maintenance to keep your system at its optimal performance.