How to Quiet a Noisy Furnace
Does your furnace remind you every time it's running, by offering you a "Bang" or a "Squeaky, squeaky, squeaky"? Sure, we are glad the furnace is on, but who wants the life scared out of them, or to have to turn the volume up on the TV to "Mega-Loud”?
More often than not, noises from a furnace and duct work are simple to fix, and can be remedied rather easily with household items or small purchases from the local home improvement store. Let's take a look at some of the noises a furnace makes, where exactly they come from, and how to fix them.
Scary Furnace Noises
Has a bang in your furnace duct ever scared the daylights out of you?
Does Your Furnace Bang Every Time it Comes On?
The wonderful "wha-boom" noise you're hearing when your furnace comes on is likely one of two things. It could be your duct work doing what’s called “oil-canning,” that is, flexing when the pressure changes, or less likely but more serious, it could be a small explosion called a “roll-out.”
Possible Cause 1: Oil-Canning Duct Work. Go to the furnace and listen carefully at different places, to see if the banging is coming from some place in the duct. If your duct is oil-canning, it likely has a weak spot and needs support.
You can easily fix this oil-canning by screwing a slightly thicker piece of metal across and onto the spot. Though it may sound silly, you could even whack that spot with something to dent it in, though I don't recommend this being your first choice.
Possible Cause 2: Ignition malfunction (roll-out). This is not very common but can be scary—a little explosion when the furnace starts up, or a burst of flame bigger than it needs to be. To see if banging is caused by a gas ignition problem, watch the furnace start up. Leave the doors on the furnace so that you aren't affecting the observation. If you can see into the furnace doors, you should be able to see what is happening. If not, listen, to pinpoint where the noise is coming from. Watch to see if the doors on the furnace shake at all. If so, then try again with the door to the burner compartment open, to see if the banging still happens and if you can see what happens when it does.
If you see extra flame or shaking associated with your noise, the good news is that you've identified a potentially dangerous problem in your home and can now correct it. The bad news is that you will most likely need help correcting the problem; messing with the gas portion of your furnace is not recommended. You may feel better to know that newer furnaces have a “roll-out sensor” that will shut down the unit if this problem occurs.
Is Your Furnace Whistling?
If your furnace is whistling, ask yourself, "Did this just start, or has it always whistled?" This will help determine what you should look for first.
Possible Cause 1: Dirty filter. Especially if this whistling has started recently, check your filter. It may be clogged and causing the fan to suck air from anywhere it can. Even tiny holes or spaces will whistle if any significant air is being sucked through them. To test this theory, pull the filter out and see if the whistling stops.
If your filter is so caked with dirt that it is clogged and stopping the flow of air, you are better off just taking the filter out (while you arrange to go get a new one). This is better not just for the noise but also for the wear and tear on your fan motor.
Possible Cause 2: Gaps in the duct. Try to hear where exactly the whistle is coming from. It will likely be a small hole near where the duct connects with the furnace close to the blower.
To resolve this problem, tape up the gaps, with foil tape or duct tape, or use clear hi-temperature silicone to seal them off.
Possible Cause 3: Ducts too small. If the whistling stops as soon as you take the doors off the furnace, it may have gone away just because you've opened up the unit and relieved the suction that was being created. If you can’t find any another cause for the noise, it could be a sign that your ducts are improperly sized; your furnace wants a greater flow of air.
Do You Have Rattling in Your Furnace and Ducts?
Vibrations and rattling are simple fixes usually. Here are a few things you can do to stop these annoying sounds.
- Add more screws to loose ducts.
- Duct-tape loose pieces.
- Add rubber or cork pads under the unit where it sits on concrete or blocks. (Yes, you can likely raise the unit with a pry bar just enough to slip something thin in there.)
Do Your Ducts Bang or Squeak When You Walk on the Floor?
Possible cause: Duct work not secured right. The duct may be too tightly secured to the ceiling below you, or the metal panning may not have been nailed up correctly. Either reinforce the duct, as with an oil-canning duct, rehang it, or replace it with "Thermo-Pan.”
Do You Hear Whooshing?
Possible Cause: Not enough air coming through. Is the air passing through the registers (the screens that let hot air into and out of your rooms) just plain loud?
You may need some duct resizing or additional return air added to your system. This will quiet things down. Temporarily, use a cheaper filter—a more permeable filter, with more and bigger holes-- and change it often to keep it clean. This will allow more air to pass through the blower.
Do You Hear Motor Noise?
Possible cause: Old motor bouncing, or wearing out its bearings. Walk around and listen to see whether the sound is coming from a motor. Try to describe the sound it’s making; this can be useful to anyone who may assist you.
In some cases, an old unit may be weak and allow the motor to sort of bounce as it runs. You may be able to place a sturdy piece of styrofoam under the squirrel cage to stop this, but if the bearings themselves are the culprit, you may need to call a professional.
There Are Many Noises a Furnace Makes and Different Reasons for Them
These tips cover most of the furnace and duct work noises I'd been called out on in my 22 years of HVAC field experience. Though most of these problems are simple to repair, the charge for HVAC service is the same whether the problem is simple or not. That’s why I try to point it out here when there is a problem you may be able to fix yourself.
Some noises aren't easily fixed. They may require professional help, depending on your mechanical abilities and knowledge. But your observations could help a professional fix them.
I invite you to describe your own issues with HVAC noises—from the furnace, A/C, exhaust fans in your bathroom, and so on--in the comments below. I will do my best to offer some advice on things that you may check and the simplest ways I know for you to fix them. We all need peace and quiet sometimes, and the last thing we need is our house yelling at us during those times.
~ We're all in this together ~
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Questions & Answers
My furnace fan makes so much noise. Would replacing its filter help with noise reduction?
Replacing your furnace's filter fan can definitely help if the filter is dirty. It's like a vacuum when it's set to "low" or when a fan tries to suck air through a dirty filter--you hear the noise difference. The difference can be more or less noticeable depending on how dirty the filter is and if the return duct is sized correctly.
When the furnace is on there is a loud low rumble coming from the vents on the other side of the house. Sounds like a train in the distance. So annoying! How can we muffle that?
First, you have to determine the source of the noise. Is it mechanical? Or is it air movement? Or is it the flames? Then perhaps it could be determined why it's only at one end of the house. Is it because that's a bedroom and it's quiet when you're in there? Is it why you only notice it there? This is what I would be checking to start.
What causes the furnace's blower motor to fluctuate in speed ?
Different modes (a/c, heat, fan) will sometimes run at different speeds while some furnaces also have features like 2 stage heating or cooling which will change fan speeds as well as variable speed and modulating units.
What causes the furnace to sound like thunder?
Perhaps oil canning in the duct. Some higher powered furnace flames can resemble a jet sound.
Our furnace (heat and AC) blows very loudly, and this was not always the case. It also wasn't a gradual change, but a sudden one. The furnace is a Payne, and just tonight I learned there is a second filter inside of the unit, which hasn't been cleaned or changed seven years. We always just changed the filter on the exterior of the unit. Could the interior filter be the issue?
© 2012 Dan Robbins