Why Is My Furnace So Loud and How Do I Fix It?

Why Is My Furnace So Loud and How Do I Fix It?

Chitty, Chitty, Bang, Bang Goes the Furnace

Your heating system is supposed to keep you warm, not keep you awake at night with a chorus of banging and clanging.

As a certified Trane dealer, we want to make sure your furnace is running smoothly!

Does your furnace remind you every time it’s running by offering a “bang” or a “squeaky” noise? Sure, we’re glad the furnace is on, but who wants the life scared out of them or to have to turn up the volume on the TV to mega-loud?

When working properly, your furnace should make nothing more than a light blowing noise when it’s on and perhaps a click or two when it switches on or off. If it’s playing a concert, there’s something amiss.

Importantly, though, if your furnace is making unusual or loud noises, you shouldn’t ignore it. You need to pinpoint the source of the sound to solve the issue. Noise can indicate a much more serious problem or even damage to the unit. Many different parts can cause noises to occur – each producing a different noise.

Before proceeding, however, we don’t want you to panic every time you hear a noise from your furnace.

When a furnace starts up to run a heating cycle, most homeowners notice some noise. This noise is typically not something to worry about. The main reason you are aware of it is that it wasn’t there a moment ago.

The bottom line: While some sounds are common when you start up the unit for the first time, you shouldn’t ignore the persistent ones.

You’ll want to troubleshoot these potential issues before they become bigger problems, especially since the chillier weather has set in.
Below, we’ll dive into what can cause each of these noises and, more importantly, what you should do if you hear them.

I have a loud banging or booming sound when the furnace is first turned on

Does a loud bang make you jump every time the furnace turns on?

If you’re hearing a loud banging or booming noise, this could indicate your furnace has dirty burners. This is hazardous as it can hinder the ignition. This delay in ignition triggers a gas build-up, producing a little explosion when it finally does light. Your burners should be regularly cleaned to avoid this issue.

Delayed ignition can be caused by several things, including an unbalanced air-to-fuel ratio. To function correctly, your furnace must contain the correct air and gas mixture. If the burners are clean, you’ll want a technician to inspect the situation. They’ll be able to make the right adjustments.

Another cause is a constrained, dirty, or clogged pilot light. For those who have an older furnace, the pilot light is what signals your burners to turn on. However, if it’s constrained, dirty, or clogged, it will fight to stay lit (or the flame may not be strong enough, which can cause a delayed ignition.)

If you think this loud booming or banging noise is coming from the furnace itself, you’ll want to contact a technician as soon as possible. It’s not safe to allow a gas build-up in your system, so this isn’t a repair you can sit on.

If your furnace is loud, you may be able to fix it by replacing your furnace filter.

What about that whistling from the furnace?

If your furnace is whistling, ask yourself, “Did this just start, or has it always whistled?” This will help determine what you should look at.

Often, a whistling sound that’s associated with a furnace is a result of a clogged air filter. If this whistling has started recently, check your filter before anything else.

How many times have we talked about the air filter in previous blogs? In fact, a clogged air filter is one of the few causes behind a noisy furnace that you can fix yourself. Just change the filter, and the noise will stop. Simple enough?

However, you should never allow your air filter to cause furnace problems before changing it. Stay on top of cleaning; it’s based on manufacturer recommendations to avoid furnace problems that can be costly. A clogged air filter doesn’t just cause annoying noise. Dirty air filters can increase energy bills and damage the furnace. They can also be fire hazards and pose health issues as well.

In addition to a dirty filter, a whistling noise when your furnace is running could indicate there is a hole where your ductwork connects to the furnace’s blower. We’ll discuss this in a bit more detail just below.

It just might be your air ducts making all the racket

A boom or thudding sound could also be the metal-air ducts contracting and expanding due to a change in temperature as the heat goes on. This is a normal activity and does not imply there’s damage. Often, this is triggered by a weak area of ductwork. Warm air from your furnace expands into your air ducts when your furnace is functioning. This added pressure on a worn section of the duct could make it to push outward and “pop.” Thus, the loud banging noise when the system switches on. The trouble can simply be addressed by switching out this piece of ductwork, or a professional may possibly add a reinforcing apparatus on the exterior of the duct.

One of the lesser-known causes of this banging sound is when the ducts under your flooring are fastened into place too securely. You may detect a banging sound when someone walks across the floor in certain spots. A heating professional will be able to loosen the duct, so it’s not so tight. It’s vital for ducts to have some “give” to them, but also not be too loose.

One more thing about ducts. As mentioned briefly above, if you hear a piercing whistling sound when the furnace is operating, it’s quite possible you have a leak in the air duct system. Unless your HVAC system is rather new, this is frequently a consequence of failing ductwork and/or poor connections to the primary duct trunk line.

The sound you hear is air leaking into your attic where it certainly doesn’t do you any good, squanders energy, and needlessly boosts your energy bills. More often than not, it will be a small hole close to a connecting point in the middle of the duct and the furnace and close to the blower.

This, too, is something that can usually be discovered and fixed during regular HVAC maintenance visits.

And, of course, be sure to keep up on your air duct cleaning throughout the seasons.

If your furnace is loud, you can fix it by cleaning your air ducts.

Or it could be a failing motor or motor belts

The fact is your blower motor or motor belts might very well be a major source of those unwanted noises.

The blower motor is designed to blow warm air out of your furnace and through the ducts in your home.

The motor in your blower unit has a belt that keeps it running. If you’re noticing a squeaking or squealing sound as your furnace operates, the motor belt could be loose or wearing out. Also, a shrill, scraping noise that seems like metal rubbing against metal can be a symptom of motor breakdown.

One such cause for this noise is that the blower wheel came unfastened from the motor shaft, shifted, and is smacking against the blower housing. If this is the case, and there is no damage to the wheel or the motor shaft, it could possibly be re-positioned back to the original spot and re-tightened to the motor.

Another, and the more likely cause, is the blower wheel broke and would need replacing. This usually produces a very alarming sound, not unlike scraping fingernails on a chalkboard.
A third likelihood is that the motor mount broke, and the complete motor and blower assembly dropped, and now the blower wheel is knocking against the housing.

If you hear this noise, it needs to be dealt with straight away. First, you should turn off your furnace right away and call a professional to do a full inspection.

Believe it or not, there can be other issues with the blower, particularly with the bearings on your blower motor. Bearings should generally last a long time on blower motors, some as long as 30 years with proper maintenance. One of the things that can cause these bearings to fail prematurely include overheating. A blower motor will get very hot if the motor is trying to turn on but won’t do so because of some blockage.

A blower can overheat from bad capacitors, which are usually a sign of poor maintenance. Whenever maintenance is performed, these capacitors are regularly checked and replaced if and when needed.

If you keep to these steps and grab hold of the problem early on, you just might be dealing with marginal damage and minor repair needs. If not, a blower fan can break completely and require a replacement. Your service professional will be able to recommend what course of action is needed.

What if my furnace is rattling?

If you hear a rattling noise coming from the furnace, it could be as simple as a panel or screw is loose. You can try to fix this yourself.

With the power off, use a screwdriver to tighten the panel screws. However, if this doesn’t fix the rattling, there could be a more critical and unsafe situation. Rattling can also be a symptom of a damaged heat exchanger with a leak or a crack in it.

You need to tackle the problem as soon as possible as it can lead to carbon monoxide leaking into your property.Contact a professional immediately if you can’t fix the rattling noise by tightening the panels and screws.

Here’s a bit more about your heat exchanger.

Don’t forget your heat exchanger

Your heat exchanger is the part of your furnace that essentially heats your home’s air.

If there are cracks in the exchanger, it can make a rattling noise when it first turns on.

Your heat exchanger is constructed of metal, so the noise you’re hearing is the sound of the crack in the exchanger expanding as it begins to heat up. One of the main reasons for a cracked heat exchanger is a lack of airflow. If the airflow is restricted from dirty filters, blowers and coils, heat can build up within the heat exchanger and cause cracks and splinters. This usually happens when the furnace has been neglected for a long period of time.

Fortunately, cracked heat exchangers are somewhat rare, so it’s unlikely your issue. However, if you think there’s even the remotest possibility that this is the issue, you want to immediately call a service technician.

As mentioned above, the cracked heat exchanger can release the gases produced during combustion into your home. Some of these gases, like carbon monoxide, are poisonous, so a professional technician should be contacted immediately if the rattling from your furnace is not squelched by tightening some screws.

If your furnace is loud, you may need to call the HVAC specialists at J&A South Park.

Fixing your furnace

It’s always a good idea to call a professional if you’re experiencing problems with your furnace. Tackling most furnace repairs yourself can damage your unit and lead to safety problems such as gas leaks.

Fortunately, not all furnace fixes require the work of a professional. You can easily replace a filter, check your flue, and oil your blower motor.

Book a tune up

A routine furnace tune-up can help avert many of these furnace sounds, such as grinding from dry bearings, squealing from a loose belt, and popping from dirty burners. Schedule an annual tune-up for your furnace with J&A South Park each year.

You might want to take advantage of a J&A South Park preventive maintenance plan for the best value. Choose our HVAC plan or customize it to include other home systems like plumbing and electrical.

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