Is Your Furnace Making Loud Noises? Easily Identify The Problem

No furnace is completely silent, but there can be certain times when the noises produced by your unit will make you wonder if something is not quite right. If your furnace is making some sound other than a low, consistent hum, you might want to take a look at this article to see if something needs attention.

Unusual sounds, particularly loud noises, coming from a furnace can be indications of various problems within the system. Gas pressure issues, dirty gas burners, a damaged belt, restricted airflow, issues with the capacitor and fan – all these things can make your furnace noisier.

Keep reading to learn details about all the different causes of furnace noise. I’ll explain what different furnace noises actually mean and what you can do to fix them. By the end of this piece, you’ll better know how to care for your furnace.

Why Is My Furnace Making Loud Noises?

Practically any mechanical device, especially one with a fan, is going to make some noise. When it comes to furnaces, the noise level is usually quite low.

furnace making loud noise

However, if you have never had such a heating unit before, it might come to you as a surprise that these systems are not silent. The only reason why you would be noticing these sounds is that they weren’t there before and as soon as you get used to the new noise, it won’t bring any discomfort.

Related: How Much Does It Cost To Move a Furnace and Water Heater?

What does a normal furnace sound like?

Normal Operation

When your furnace is working, it’ll make some noise. This sound should be hardly noticeable unless you’re right next to the furnace. Furnaces make a quiet rumbling noise as they burn through fuel to heat your home.

Also, you’ll hear the soft purr of the blower motor spinning. If your furnace is making noises other than a quiet rumble, it’s likely one of the problems we’ll be covering below.

Some units are going to be quieter than the others, but all-in-all the sounds of a correctly operating furnace shouldn’t become an inconvenience to you.

What Does a Bad Furnace Sound Like?

You might be asking yourself ‘when should I worry about my furnace noise?’.

As a rule of thumb, any unusual sound can become a cause for concern. It might indicate that there is something wrong with your furnace.

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Here are some different sounds a furnace can make and what causes them:

Humming sound

If you hear a low hum, then there is nothing to worry about. But if it has become louder or uneven, then there might be an issue with the capacitor or blower fan.

This will likely take an experienced technician to diagnose properly. Next time you have your system maintenance check, ask the tech to listen specifically to the hum. Let him know it hasn’t always sounded that way.

Banging sounds

A loud boom can be caused by a small ‘explosion’ that occurs when there is an ignition delay. When the gas burners do not ignite on time, the gas has a few spare seconds to build up in the chamber.

This happens either because the gas burners are dirty or because there is a gas pressure issue. In any case, a professional should take care of such an issue.

You might also hear popping as soon as you turn the furnace on. This happens when heated air hits the cold ducts.

The slight expansion of the ducting materials will often times make clicking and creaking sounds. But this should stop after a few moments.

furnace gas valve assembly

Read: Best Furnace Flame Sensors

A high-pitched squealing noise

You’ll hear a shrieking noise if there is a problem with the motor. It might be because of a damaged or loosen belt. Fortunately, this is a relatively easy fix.

Unfortunately, squealing sounds can also be indicators of a more serious problem with the actual motor.

furnace blower belt

rattling noises

This happens when one of the parts within the heating system becomes loose. The vibration caused by the components is what makes a rattling noise.

If a screw, washer, nut, or other component comes loose within a furnace, it’ll be tossed around when the machine operates. If a piece is loose inside a furnace, it may harm other components within the system. 

Rumbling Noise (Sounds Like a Dryer)

You might hear a thump or vibration that will make your furnace sound like a dryer. The chances are high that, in such a case, the blower wheel is imbalanced

If the rumbling continues even when the furnace finishes a cycle, it might be because fuel is continuing to burn in the chamber (even though the burners had already shut down).

Read: Furnace Blower Motor Makes Noise When Starting – Troubleshooting Guide

Whistling sound

Furnaces make a whistling noise when they have restricted airflow. The whistling noise is caused by air being forced through a small hole in a blocked pipe. Poor airflow can harm your furnace’s effectiveness and cause damage to other components.

Related: How To Increase Airflow in Ductwork

In the majority of cases, all you would have to do is change the filter. At times, the airflow can also be restricted by dirt in the grilles and air handler.

Read: How Often To Change Furnace Filter?

Furnace Sounds Like a Train Whistle

This high-pitched noise might also remind you of an airplane.

A leak in the ductwork might be causing such a sound or the blower motor bearings that have become worn out.

How Do You Fix a Noisy Furnace?

As you might have already figured out from all the issues mentioned above, it is better to call a professional whenever you hear your furnace make a strange noise.

Usually, these annoying sounds indicate serious problems with the furnace’s components, so leaving that to an expert might be the best decision.

However, there are a few simple things that you can do to try to get rid of the noise problem on your own.

Check the Ductwork

If you hear a banging or popping sound coming from a certain place in the ductwork, then you can attempt strengthening this weak spot.

ductwork in attic

For example, you can screw a piece of metal that is slightly thicker than the duct across and onto the existing metal.

Related: How Hard Is To Replace Ductwork?

If you hear a whistling sound, then, once again, try to figure out where it’s coming from. Your ductwork can have a few gaps or you might find a hole in the place where the ducts connect to the furnace.

In any case, use foil tape to seal all these leaks.

Fact: Up to 30% of air gets lost in the ductwork due to holes, leaks, and poorly connected ducts. 

Finally, whistling can indicate that your ducts are simply too small. If you have a powerful furnace, it might require a greater airflow that the ducts are not able to let through.

Replace the Filter

The easiest way to fix a whistling noise problem is to simply replace a dirty filter with a new one.

Remove the filter to find out if this is the thing that is causing the sound. If yes, then remove the clogged component and insert a brand-new filter.

dirty furnace filter

Related: Why Does My Furnace Filter Get Dirty So Quickly

You should replace your filters at least once every 90 days, but sometimes it has to be done a bit more often.

Check Ignition Malfunction

You are not going to fix the problem if you follow the steps below, but you are at least going to have an understanding of what’s going on.

  1. Try seeing into the furnace doors during the furnace start-up.
  2. If you can’t really see anything, then listen (you might hear a bang) and watch to see if the doors are shaking.
  3. If you have spotted any extra flame, a banging sound, or the doors were shaking, then there is a serious issue with the gas ignition.
  4. This problem can potentially be dangerous, so call your HVAC expert right away.

Hint: Newer furnaces shouldn’t have such a problem at all as they feature a ‘roll-out sensor’ that prevents such an issue from occurring in the first place.

How to Quiet a Noisy Furnace Blower?

Here are the things that you can do to reduce the noise coming from a furnace blower.

Build sound insulation

Most of the noise is coming from the blower intake, so you can use melamine foam to insulate this part of the system.

You would have to use a steel wire to secure the foam in place, but all the efforts might be worth it.

Consider getting a variable-speed blower

Such blowers are practically silent (unlike single-speed blowers). As a bonus, variable-speed models will help you reduce your heating bills and will help make sure that your house is heated more efficiently.

Add return air ducts

You can easily check if the blower has insufficient return air. Simply open the air filter door, and if that had made the whistling noise go away, then you should definitely consider adding a few return air ducts.

You would have to invite a professional to help you with that.

Adjust the fan speed

This is a simple trick that can do wonders.

Try decreasing the fan speed and then check the airflow. If you feel comfortable in your house even with a low-speed fan, then leave it that way.

Replace the loose parts

Loose fins on the blower or a loose belt can be causing a lot of furnace noise problems. It might be much cheaper to replace the part than to continue putting up with the noise.

When Should You Worry About Furnace Noise?

Now that you’re aware of the common causes of noise in furnaces, it’s time to figure out what noises should be a cause of concern. Especially because some amount of noise is expected from your furnace. So when should you worry about the noises coming from the furnace in your home? 

You should worry about your furnace when it makes any noise other than a quiet hum. Furnaces make a quiet rumbling noise when in regular operation. If your furnace is making any loud banging, scratching, whistling, or screeching noises, it’s likely due to a major issue in the system. 

inspecting loud noises in furnace

Modern furnaces are designed to run extremely quietly. Many modern furnaces are installed in people’s kitchens, and you wouldn’t know it was there until you opened the press and saw the unit. 

However, older furnaces aren’t particularly quiet, and you can definitely tell when it’s on.

If your furnace is making noticeable noises that it’s never made before, it’s likely due to damages, blockages, or other issues happening within the system. The only noise your furnace should make is a quiet hum when it’s running a cycle. 

Furnaces are heating components that usually burn gas or flammable liquids to operate. Therefore, a furnace that’s not operating effectively could catch fire, explode, or leak harmful gasses into your home. Therefore, you should have your furnace repaired as soon as you hear any sort of unusual or loud noise coming from it.

Read: How To Clean Gas Furnace?

How To Prevent a Noisy Furnace in the Future?

Now that you know what to do when your furnace becomes noisy, why your furnace is making noise, and when you should worry about furnace noise, it’s time to figure out what you can do to prevent noise problems in the future. 

So, how can you prevent your furnace from becoming noisy? 

To prevent a noisy furnace in the future, you can opt to hire a qualified person to service the furnace every year. They will clear airways and lubricate moving parts to reduce noise permanently.

That said, if you want to learn how to do the maintenance yourself, that is absolutely possible. Guides like this one and many others can be a great resource to becoming self-reliant in regard to the various systems in your home.

Read: What Are Common Furnace Repair Problems?

Final Thoughts 

Furnaces make a quiet hum sound when they’re in good condition and operational. Usually, if your furnace is making loud noises, something is wrong and needs repair.

Furnaces can make several different types of sounds when they’re damaged. Your furnace may whistle, bang, bump, grind, or rattle, depending on the root of the issue. Whenever your furnace is making excessive noise, you should look into as soon as you can.

If you’re inexperienced and unconfident in your own abilities, I would recommend hiring a professional to assess and fix the damages, as repairing a furnace can be dangerous – both to you and your home.

However, there are many things a DIYer can do themselves to maintain and repair their furnace when it eventually has an issue. Just be sure to do your homework and don’t try to take shortcuts.