When you consider the mechanics of an HVAC system, it seems like the kind of thing that could make some noise: heating up a bunch of air and pushing it through enclosed ducts so it can be delivered around the home could alarm any homeowner. But we’re often surprised when we go on routine furnace tune-ups and hear awful noises that the client has either given up on fixing or doesn’t notice anymore. “I thought it was supposed to sound that way” is a common refrain in this situation. Furnaces can be loud at times, but that’s not the last word on the subject. There’s a lot we can do to make your furnace and ducts quieter, and if the noise is getting to you (or getting worse!), it’s worth getting a contractor for your sanity and the health of your system.
The Old Furnace Rattle
Most people thinking about noisy furnaces probably remember the scene in “A Christmas Story” where Ralphie’s dad goes down to the basement to deal with a “clinker” that’s causing a racket. As funny as the scene is, you won’t be dealing with a clinker if you have a modern forced-air furnace in your home because your furnace doesn’t work that way. Your noises are going to be something else entirely.
Awful metal-on-metal noises require immediate attention. These noises could vary, but anytime you hear something truly horrendous, it’s time to turn off your furnace and call your HVAC contractor. Something has broken inside — probably the blower wheel — and needs to be fixed or replaced. Serious, serious damage is occurring or will occur if this is not addressed.
A squealing or high-pitched whine is a sign of an aging furnace or worn-out parts. It’s not as serious as other issues, but your furnace should be examined anyway. That way you’ll know how long the furnace has left or if you can do anything to prolong its lifespan. Keep in mind that any furnace made more than ten years ago has a lifespan of 10-15 years at the most. Furnaces made recently, however, are designed to get at least 20-25 years of use if they’re maintained properly.
Another common noise is a popping or ticking noise as the furnace heats up. This noise in particular can be tricky to figure out, because it could be a lot of things — a loose fan, a worn motor bearing, a problematic gas valve, or maybe just undersized air ducts. If it’s the fan, it could be a problem and result in the metal-on-metal noise we just talked about. A bearing that’s going bad can be fixed unless it goes on too long and the motor burns out — this isn’t a cheap fix, so you the sooner you replace a bad bearing, the better. Too-small ducts aren’t as immediate of an issue, but it will shorten the lifespan of your furnace, often by a few years or more.
If your furnace is newer, it’s all the more reason to get strange noises taken care of. With newer furnaces, it’s usually cheaper to fix than to replace, and you’re less likely to have to replace it if you take good care of it. Older furnaces may be a different story—some things can be fixed, but some can’t or are so expensive to fix you might as well get a new furnace. Your mileage will vary, and that’s why it’s important to work with a trusted contractor when dealing with these issues.
It’s in the Air Vents!
Just like the alien in the movie Alien (or every Mission Impossible film), bad things can happen in the ducts. A “furnace noise” might actually be a duct rattle or shake that’s occurring close to the furnace. These rattles and noises can also occur far away from the furnace and can sound pretty weird. If you’re hearing furnace noises across the house from the furnace, it’s probably an issue with the ducts.
As with furnace noises, however, these duct noises can have many causes. It’s hard to pin down one reason when debris, vibration, and lack of air flow could all be the cause of the noises. Temperature and pressure difference are often the biggest culprits, and they’ll make your ducts vibrate like a tuning fork or bang like a gun. An HVAC contractor is the way to go with this one. They’ll figure out what the problem is and fix it, or at least point you in the right direction so you can decide how to proceed. Like furnace noises, not all duct noises are a death knell, but well-maintained and well-designed duct systems should not make much noise.
Sherlock Holmes never ignores a clue, especially the ones that other people miss. Furnace noises are easy to miss because we just get used to them. But the next time yours comes on, pay attention and see what it’s trying to tell you. Sometimes it will be screaming for help, and sometimes it’s just very quietly drawing your attention. But no matter what the strange noise is, it needs to be checked out by a pro. These are the warning signs that things can get worse (and they will eventually get worse) if they aren’t dealt with by an HVAC company you can trust.