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How to Quiet a Noisy Furnace

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Dan has been in the HVAC industry for 23 years with experience ranging from installation and service to sales and distribution.

Furnace Blower Motor Makes a Noise When Starting

Does your furnace remind you every time it's running by offering you a "bang" or a squeaky, squeaky, squeaky noise? 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 ductwork 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.

Why 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 ductwork 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.”

1. Check Oil-Canning Duct Work

Go to the furnace and listen carefully at different places to see if the banging is coming from someplace 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.

2. Check 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 to correct 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.

The return air drop, a common location for oil-canning, is on the side of this furnace; in a furnace that blows downward, the return air drop will be connected to the top.

The return air drop, a common location for oil-canning, is on the side of this furnace; in a furnace that blows downward, the return air drop will be connected to the top.

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 cause 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 quality HVAC foil tape. Duct tape or clear hi-temperature silicone can be used in a pinch to seal them off. Foil tape tends to work very well, and if you take some extra time to seal the various junctions in your ductwork while you're there, it'll even help make your system more efficient. I suggest you use foil tape like this one by Impressa Products. Foil tape can take the heat in your ducts a lot better than standard duct tape can.

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 other cause for the noise, it could be a sign that your ducts are improperly sized; your furnace wants a greater flow of air.

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Read More From Dengarden

This is the perfect example of a "whistler" gap in duct work.

This is the perfect example of a "whistler" gap in duct work.

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.)
Squeaks and vibrations are common around the duct hangers.

Squeaks and vibrations are common around the duct hangers.

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.

Blower Motor and Housing

Blower Motor and Housing

There Are Many Noises a Furnace Makes and Different Reasons for Them

These tips cover most of the furnace and ductwork 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.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: Air rushing in my furnace and making a loud noise. Is this normal?

Answer: It’s not necessarily normal but it’s common. Often the return duct size needs increased.

Question: I hear a whining noise at the end of the furnace's heating cycle. Would this be a light oil or belt replacement?

Answer: Neither would hurt. Perhaps check amp draw on the motor. If it's high it might be on the fritz.

Question: Our furnace venting motor is noisy. I was told that it would be $1500 to replace but that as long as it continues to work there is no need to replace it unless the noise is bothersome. Can this be repaired or is the replacement the only solution?

Answer: $1500 is an insane amount of money for an inducer motor. These aren’t hard to replace even if a kit repair is needed. The most expensive motors and motor kits are around $600-800 in the highest end of furnaces and $700-900 in labor is robbery. An average furnace inducer motor assembly is around $200-300 and takes maybe 2 hours to replace. Please get a second opinion.

Question: My furnace makes chirping sounds about 2 1/2 minutes into the furnace cycle up. I have already replaced the blower venting motor, the inducer housing assembly, the Flame sensor, and igniter. There are new batteries in my thermostat. I still get the chirping sound then the furnace cuts off. I have a new filter installed as well. It's driving us nuts. What could it be?

Answer: It’s possible the issue is the blower motor or better yet the wheel itself. If it’s out of balance or the shaft is wobbling that could be the problem. Perhaps it’s a combination of all those things, and a blower assembly may be needed. I can never guarantee an online diagnosis, but this is what I would be looking at.

Question: We just had a new HVAC unit installed. I was not sure if the old unit was a 3 1/2 ton or 4 ton, so we went with a 4 ton. Now the return air fan, which happens to be just across from the bedroom, is so loud we cannot sleep at night. It does pull more air through it than the old unit did. Is there anything we can do to quieten it down?

Answer: Well, you may ask them if they can slow the fan, but it has to carry a certain amount of air for the A/C to work. Since you opted to go with 4 tons, you needed more air. Your contractor should be the one telling you what size you need based on math. Not a guess. Rule of thumb is to go smaller with an A/C if it’s close, not bigger. Bigger is also likely to “short cycle” where a smaller unit that runs more but starts and stops less often is actually more efficient and does a better job of dehumidifying which is what an A/C really is, a big dehumidifier.

Question: 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?

Answer: Yes, it is very possible and if it’s been that long it may have taken a toll on the motor. I would change and clean that filter.

Question: My AC/furnace started making noise a few days ago. It has progressively gotten louder and louder. It definitely sounds like the motor or even the fan blades are clanking. When I stand outside the unit, it is definitely where the noise is coming from. The blower motor is still working, but it does not seem like it is blowing as hard as it should. Will a simple cleaning of the motor and replacement of the filter fix the problem?

Answer: I’m not sure what the clanking is, but if the outdoor unit is malfunctioning it could cause the indoor coil to freeze and restrict air flow. While I never turn down good maintenance practices, I don’t think that is your problem.