Home furnaces are noisy by nature, with their large blower, expanding hot air, metal compartments and other parts. And let’s not forget the array of burners we are all too aware of when one fires up.
A noisy furnace could be giving you loud vibrational noises, high-pitched squeals or just general motor and air noise that sounds like a 747 is about to take off from your basement or garage.
It could also be humming or whirring, which results in your furnace not running and heating as it should.
Since there are several parts to your heating system that could be causing a noisy furnace, let’s take a look at each one and see what methods and/or repairs are necessary to make it quieter.
Causes for a Furnace Making Noise
As just mentioned, many different parts could be responsible for a furnace that is noisier than normal.
The motor for the blower makes noise as it works to spin the fins, which get air moving.
Gas burners inside gas furnaces, ignite and fire as gas flows in. Metal air chambers such as your furnace plenum and attaching duct work all contain fast moving warm air.
And finally, all this working together can vibrate all or part of your furnace.
And as it’s adjacent to and/or attached to walls and floors, the vibration can transfer, causing even more noise to emanate from structures in your home.
Yes, it can be hard to initially tell just which of these parts is lending to your noisy furnace.
The good news is that you can usually narrow it down by the type of noise you’re hearing. Review the following to help you determine this.
“Air noise” coming from furnace:
Generally, airy noise from your furnace is normal for obvious reasons.
But if you have an unusually noisy airy sound from your furnace (i.e. it keeps you awake at night!), then you may have air leaks around where your furnace meets the plenum (the chamber where your main duct connects to).
Check to see that any seams here are sealed. You may see tape already there, but it could be coming lose and allowing air to whiz through when the furnace is running. Retape with duct tape if necessary.
“Train” noise coming out of furnace:
While the motor and fan inside your furnace makes considerable noise, you don’t exactly want it to sound as if you’re standing next to a train when you go up next to it.
Make sure that your furnace filter is clean and isn’t restricting airflow by being dirty.
You can also check if other restrictions in the system are present and causing your furnace to work harder than it should.
If too many vents are closed or covered up in your home, is one culprit for this. Just check that good airflow is occurring at several of your registers in the home.
You may have directional flaps that route air in some of your duct work. Check that these are not fully closed and in fact are doing their job of dividing and moving air accordingly down your duct work.
Furnace hums when trying to start:
This may be an issue with the capacity in your HVAC unit. If it’s gone bad and can’t hold a charge anymore (to help the normal jumpstart the your blower motor), then it needs to be replaced.
You can test your capacitor to see if it’s holding charge or simply replace if you have an older furnace. This is usually the cause for a furnace making noise at startup, but not coming on.
Furnace clicks and won’t start:
This may be a problem with the furnace transformer. It may not be converting the voltage from your home’s electrical system correctly, and thus, supplying the wrong voltage to your furnace to start it up.
A simple test of the transformer can help eliminate this cause for this abnormal noise with a furnace.
Furnace makes “high pitch or squealing” sounds:
With this type of furnace noise, you may need a minor tune-up. In particular, you’ll most likely need to adjust or replace a worn or misaligned drive belt.
It’s always best to follow the directions in your furnace manual for maintaining a drive belt, i.e. it can tell you how to properly set the tension for it.
You can access your drive belt through the main access panel on the front or side of your furnace–where this type of furnace noise will be coming from.
When you get a hold of the belt, see that it doesn’t have any cracks and is not fraying. If the belt’s condition is in question you should replace it.
Follow the directions in your manual on how to remove the belt. Check the alignment of the belt by holding a straight edged item (ruler) against the faces of both belt pulleys and match it against the belt.
You want the belt to be aligned to it. Again, follow the directions for adjusting this alignment in your manual, if necessary.
Your manual can also tell you if your furnace motor needs oil or not, and how to oil it.
Oil can definitely help with this type of furnace noise! If you don’t have your manual, call the manufacturer and have them send one, or have a technician from the maker guide you.
Lastly, if your belt is fine, this furnace noise may be indicating that the motor’s bearings have worn out. Call a technician if in doubt to accurately assess.
“Lower pitch” noise coming from wall or floor on other side from furnace:
If you’re in another room from the furnace and you hear a lot of noise (like a motorcycle is idling on the other side), it’s most likely because the furnace is not secured well enough to the floor or wall.
Check that all screws, bolts and braces are tight and firm against walls. Check that supporting walls are solid and not damaged.
If so, you may need to replace them, so your furnace cannot vibrate as it runs.
FAQ – Noisy Furnace Troubleshooting
How Do I Make My Furnace Blower Quieter?
As described above, there are many reasons why your furnace could be loud.
To troubleshoot, start by checking and replacing air filters, cleaning the dust buildup from, and inspecting blower belts.
All of these can cause your blower to be working harder, thus a louder sound from the physical blower motor.
You can also look into replacing older parts such as the fan bearings or an old motor. Some furnaces allow you to turn down the speed which could help with the noise.
If everything looks good, but it is still loud you can insulate with melamine foam to block a lot of the blower air and motor noise.
What Does a Bad Furnace Sound Like?
Furnaces will always make some type of noise when starting up. Usually, this noise includes a quick popping sound followed by the blower fan kicking on.
Your furnace should be making a low humming sound in general while it’s running.
Any other types of noises such as squealing, thumping, grinding, or rattling sounds during start-up, run time, or shut down are potential signs of a bad furnace.
Are New Furnaces Quieter?
Technology has come a long way in the last 30 years!
Furnaces used to be large and loud. Today, new furnaces are generally quieter and more efficient than their outdated counterparts.
The quiet feature in most new furnaces is because they are two-speed or variable speed when operating. This means that the fan can blow on a high and low setting which can be quieter than traditional single-stage furnaces.
Also, furnaces today are generally just built better with noise reduction and insulation taken into account.
When your furnace makes noise, it may not be normal. Identify the type of sound, then take needed action to keep you and your family warm in the colder months.