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Furnace Making Noise? It’s Probably Not a Poltergeist

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Last Updated on March 12, 2019

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It’s downright scary when your furnace is making noise

It’s Halloween again, that spooky time of year when you see ghosts, bats and witches hanging out all around your neighborhood (not to mention miniature superheroes and Disney princesses). So when you have a furnace making noise and producing all sorts of ominous sounds, you can’t help but wonder if a poltergeist is haunting it.

Before you call in the ghost busters, get a grip and realize that your furnace is making noise because something is wrong, and more than likely it’s not an evil spirit.

Here are some clues to the common problems that cause your furnace to be making noise. Luckily, most of them are not that scary.

FURNACE MAKING NOISE: The Whistle

That creepy whistling that sounds like a banshee is really an air flow problem in your ventilation system. Some possible causes:

Dirty filter. Is your furnace’s air filter clogged with dust and debris? Probably so if it hasn’t been changed in a while, and your system is not getting adequate air flow. When that happens, you get pressure problems that result in your furnace making that noise that’s haunting your dreams. In this case, there’s an easy fix: replace the air filter and that whistle will vanish.

Related article: Fall Furnace Maintenance: How to Change Your Furnace’s Air Filter

Leaky ducts. If you have an older HVAC system, holes and cracks can develop in your ventilation ducts over time. Eventually you’ll hear the eerie sound of air being forced out through those holes and cracks, and you may think it’s your furnace making noise. This fix is not quite as easy as replacing the air filter, but it’s usually just a matter of repairing your ducts to restore peace and quiet to your space.

Ducts are too small. If you replaced your furnace recently, you’re probably alarmed to be hearing your furnace making noise already! But if you replaced it without updating your ventilation system, your ducts may be inadequately sized to handle the volume of air from the new system. You’ll need a certified HVAC expert to evaluate your system’s air flow requirements and install the correct size ducts.

Is your furnace blowing cold air and making noise? Read this related article: Furnace Blowing Cold Air? 13 Common Causes

FURNACE MAKING NOISE: The Rattle

When your furnace is making this noise, all the shaking may make you wonder if there’s an impending earthquake or a zombie apocalypse. The first step to diagnosing the cause is determining origin of the sound. Do you hear it coming from the furnace or the ventilation system? You’ll probably find it’s the latter. Call in the experts to banish this noise from your space.

Loose ducts. If your ventilation ducts are not securely attached to the wall, floor or ceiling, you may be hearing that rattle and assume it’s your furnace making noise. In reality, your ducts’ fastenings may have come loose over time due to vibration from the system. The pressure of air blowing through can cause those loose ducts to shake and rattle. If you don’t mind climbing around in the crawl spaces, you may be able to find where the duct has come loose and fix this with a screwdriver.

Something’s in there. No, not a ghost! If you have mischievous children in the building, or possibly even rodents, it’s not unheard of for unusual objects (like marbles, or acorns, or action figures) to end up in your ducts causing that mind-numbing rattle that you can misinterpret as your furnace making noise.

Your furnace is unstable. If it’s not the ducts and your whole furnace is not just making noise but shaking, then it needs stabilizing. Buildings shift and settle over time, and the bolts that attach your furnace to its surface may be loose. Don’t attempt to fix this problem without professional help! Your furnace is a combustion appliance, and probably has a gas line that’s dangerous if tampered with. Let the experts take care of this.

Bearings are wearing out. If you hear the rattle coming from the furnace motor, the motor bearings may be worn out and need replacing.

FURNACE MAKING NOISE: The Squeal

Have you been neglecting furnace maintenance? If it sounds like a tortured spirit is living in your furnace and making noise, it may have developed service issues. Here are some common causes.

Related topic: 4 Consequences of Fall Furnace Maintenance Neglect

Failing blower belt. The belt that drives the blower motor may have slipped, come loose or it may be worn and needs replacing. If you had remembered to do your furnace preventative maintenance, your furnace would not be making this noise, because that belt would have been repaired long before it started making that annoying squeal.

Motor shaft bearings need lubrication. Again, you can prevent this cause of your furnace making noise by signing up for regular HVAC maintenance. Your furnace’s moving parts need to be oiled every so often so they continue to work efficiently and quietly.

FURNACE MAKING NOISE: The Bang

ALERT: When your furnace is making this noise, it could potentially be a dangerous situation. Are you hearing a loud bang when your furnace starts up? Don’t fool around with this one; call an HVAC expert right away. You might have a problem that could be deadly if neglected.

Here are some possible causes of your furnace making this noise:

Gas ignition problem. That “bang” might be a small explosion that happens when your furnace ignites. The problem could be caused by a faulty electronic ignition or by dirty burners that delay the ignition and cause gas to build up before it finally ignites. Get it checked out immediately, since the little explosions can crack your heat exchanger, allowing carbon monoxide to escape into the air you breathe. A cracked heat exchanger also means you need a new furnace.

Expanding ducts. You may hear your furnace making this noise due to weak spots in your duct work. When the furnace turns on, pressure changes can force ducts to “pop” or expand in the weak areas. That banging and popping will go away when you repair the weak spots in the ducts.

Are you starting to see a pattern here? When your furnace is making noise, many of those scary (or at least downright annoying) sounds are caused by neglected maintenance. Even the worst-case scenario here (the gas ignition problem) would be prevented if the furnace was regularly cleaned and inspected.

So there’s no need to call in the ghost busters to stop your furnace making noise. Instead, call in a qualified HVAC service company to get rid of those spooks in your system, and keep it running efficiently and reliably.

Your peace and quiet is only one of the many things you risk when you fail to regularly maintain your HVAC equipment. Poor maintenance also costs you in many ways that you may not realize. Want to learn more? Grab a copy of our helpful guide to Calculating the Hidden Costs of Poor HVAC Maintenance.

Get the guide to understanding your HVAC System's hidden costs.