SERVING 
Furnaces occasionally make weird sounds.
From high-pitched whines to annoying thumps, furnaces are capable of producing all sorts of worrisome noises. Some of these sounds don’t mean there’s anything wrong with the furnace. Others, however, do indicate the presence of a problem.
Let’s take a look at some of the reasons why your furnace might start making noise. We’ll consider the sounds that indicate a problem, sounds that don’t necessarily indicate a problem, and some solutions for dealing with whatever you’re hearing.
1. Bumps and knocks
Maybe you’ve never had a problem with your furnace. Then one evening, you’re getting cozy in your living room when you hear it:
*Knock* *Knock* *Knock*
Or maybe it’s not a knock. Maybe it’s a bump. Or a kind of dull clang.
Regardless, your furnace is doing something weird and it doesn’t sound good! When this happens, it’s usually because the blower wheel is off balance and has started knocking around. You’ll notice that the furnace makes noise when starting up and continues to knock throughout each heating cycle.
If you encounter this problem, you will need to call an HVAC pro to repair the blower assembly. In most cases, this problem requires a new blower wheel, which will need to be installed by a technician. Your technician will remove the blower assembly from the unit and install the new wheel. In the process, he or she will clean the blower before reinstalling it.
After that, you shouldn’t hear anything go bump in the night… at least not from your furnace.
2. High-pitched whine
That’s not a banshee in your furnace. It’s the bearings in your inducer fan motor.
The inducer fan is a nifty little component that clears gasses out of your furnace’s heat exchanger following a heating cycle. Over time it wears out. Sometimes the first sign your inducer fan is failing is a high-pitched sound coming from the bearings. When you hear this, it usually means the motor is about to fail. The only fix is to replace the inducer fan motor.
At the time of writing, it costs anywhere from $600 to $800 to replace an inducer fan motor. If you’ve got an older HVAC system that you’re considering replacing, it’s probably more cost effective to just replace your HVAC system instead of swapping out the inducer fan motor.
3. Whistling
If you hear a whistling sound, it might not be your furnace. Check your return air grille. If the whistling is louder right next to the grille, that’s probably all it is.
First, clean the grille fins. If you still hear a whistling sound, you may need to open up the grille fins so that there are wider spaces between each one. Use a good pair of pliers to make small adjustments to the fins until the whistling sound abates.
4. *Whoof* *Fwaaah* *Chug Chug Chug* etc.
Sometimes, you just hear everything your furnace is doing. First, the furnace makes noise when starting up. Then it makes even more noise as it runs. This can get really annoying when you’re trying to relax, read a book, watch TV, or just hang out with the family.
When we hear about furnaces that are just noisy in general, it’s often in apartments or condominiums with a central air return. The furnace in these spaces may be located in a utility closet, meaning it’s basically inside the occupants’ living space. You’ll hear the furnace pretty much any time it’s running a heating cycle.
To address the problem, have your HVAC company install a muffler-style grille in place of your existing return air grille. These specialty grilles are designed to block the noises from your furnace while ensuring that the system still gets enough return air.
Variable speed furnaces are quieter all around
If you’re replacing a furnace and want an all-around quieter unit, consider a variable speed furnace. Unlike standard “on/off” units, variable speed furnaces modulate among different heat stages. Most of the time, they run at a very low speed and only ramp up on colder days or times when your home needs more heat.
As a result, they’re much quieter! The low speeds mean less air is moving through your ducts. Also, the blower doesn’t make as much noise because it’s rarely running at full blast. If you’ve got the whistling problem or the “generally noisy furnace” problem described above, a variable speed furnace could help a lot!
Hearing something weird from your furnace? We’ve got you.
At PV, we service misbehaving furnaces all across the Metro Atlanta region. If your furnace is making weird sounds or otherwise giving you trouble, give us a call at (404) 798-9672 or schedule service online!
