Weird Furnace Sounds and What to Do About Them

Don't Be Scared by Weird Furnace Sounds, We've Got Your Back

Did you know that the furnace is one of the greatest inventions that changed the world? After all, it's the machine that made mass production of steel possible.

In buildings, though, furnaces do more than provide comfortable heat. They can be life-savers, as they help reduce the risks of detrimental cold weather hazards. This is especially true for hypothermia, a medical emergency.

On the flip side, a faulty furnace can also be a safety risk, what with the heat and gases it creates. Weird furnace sounds are often an indication of a malfunctioning system. The odder, louder, and "scarier" these noises are, the greater the danger they may bring.

To that end, we at Technical Hot & Cold came up with this guide on furnace noises and what they usually mean. Read on to learn all about them (plus tips on how to put a stop to the racket they make).

Wheezing Or Whistling

You know how having a cold can result in a whistling sound while you breathe? Those sounds come from the air trying to get past your blocked, inflamed, or tightened airways.

Your furnace can make a similar whistling sound if its filter gets clogged (with filth), too. Dirt and debris build-up restricts the air from passing through the filter.

A dent or deformation in your furnace filter can also create a wheezing noise. This can happen if the damage compresses a section of the filter, resulting in a blockage. Since the air can't pass freely, it can generate those weird whistling sounds.

Fortunately, most wheezing furnace cases are easy to fix: you only need to swap the old filter with a fresh one. However, be sure to check if your existing filter is reusable, as you may only need to wash it instead of replacing it. Even if you do need a new filter, don't worry, as these are some of the most widely available HVAC parts.

A Loud Boom

Did you hear your furnace boom or pop soon after turning it on for the first time after a long period of rest? If so, those noises were likely due to your ductwork's metal parts expanding. After all, the "resting" (or cooling) phase made the metals contract.

These booming or popping sounds should dampen or mellow out the longer you run your furnace. If they don't, or they even get louder, you may be dealing with "delayed ignition". This can be caused by clogged burners, pilot issues, or gas pressure problems.

Unburned fuel can build up gas, which, in turn, can make a loud booming sound once ignited.

Routine HVAC maintenance can help ensure your gas furnace turns on without a hitch. A critical part of these tune-ups is the inspection and clean-up of furnace burners. Our furnace techs at THC also check the condition of your system's ignitor and flame sensor.

Shrill Squeals

A furnace squealing or wailing often indicates shaft bearings that lack lubrication. This, in turn, creates excess friction, hence the irritating noises. You can easily prevent (and fix) this by getting your furnace inspected before the season.

Another common culprit behind those screeches and squeals is a defective or dry fan belt. The belt may also have become too taut, out-of-place, or misaligned. Aside from lack of maintenance, these issues may also result from normal wear and tear.

The worst-case scenario is that your furnace's blower motor itself is about to kick the bucket. This could happen if the motor has overheated numerous times before. Overheating, in turn, can be due to filth accumulation or a damaged fan belt.

Since these noises can arise from various culprits, a DIY inspection may not be the smartest move. The easiest way to figure out the cause of those squeals is to get a professional HVAC diagnosis. From there, your THC tech can proceed to fix your boisterous heater.

Ear-Piercing Scraping

If these are the kind of noises your furnace makes, shut it off right away, and contact a licensed HVAC professional at Technical Hot & Cold right after.

For starters, furnace metal scraping sounds may sound like nails on a chalkboard. That should be enough reason to turn your heater off to silence the dreadful noise.

More than that, these sounds are more than likely to be actual metal grinding against metal. If you let this go on, your blower fan/wheel may become so damaged it would need a replacement.

At the very least, these bothersome furnace noises may be due to bearings that have become so dry or worn out. As a result, they can no longer do their part of reducing friction between your furnace's moving parts.

Another possible culprit is an askew or loose furnace blower fan. In this case, the fan may be hitting and then grinding against the blower house casing.

Hissing With a Touch of Rotten Eggs

Michigan is a big natural gas user, with about 80% of households using it as their primary source of heating fuel. If you're part of this crowd, it's best you know how to detect natural gas leaks.

Natural gas itself is odorless, so it's impossible to detect without special equipment. That's why gas suppliers tinge it with mercaptan, a gas that smells like sulfur. The scent of sulfur resembles that of rotten eggs.

You may have a gas leak if these odors permeate your home and your furnace (or a gas line) makes hissing sounds.

In this case, turn off both your furnace and gas supply as soon as possible. If you can, open some of your windows before you leave your home. Only after you're outside should you ring up your gas provider or emergency services.

Although not common, natural gas leaks can cause explosions.

Rattling With a Hint of Pickle

A furnace relies on a heat exchanger to "seal" combustion gases inside a chamber. You can think of the exchanger as a shield (it is a sheet of metal, after all). As a "shield," it keeps toxic combustion gases trapped within the combustion chamber.

Unfortunately, a furnace's heat exchanger can develop cracks due to thermal stresses. If this happens, you may hear rattling sounds from the system. Worse, such issues can lead to the leakage of dangerous gases into your home.

Do note that rattling can also occur due to loose fasteners like screws, bolts, and nuts. However, if these noises come with the smell of pickles, you likely have a cracked heat exchanger. These odors are usually attributable to the aldehydes that combustion gases contain.

An even more dangerous gas that can leak from a cracked exchanger is carbon monoxide. CO is particularly dangerous because it's invisible, odorless, and tasteless. It's highly toxic, which is why exposure to it lands about 50,000 people in US emergency rooms each year.

Stay on Your Toes for These Weird Furnace Sounds and Woes

As you can see, abnormal furnace sounds can take many forms, from wheezing to hissing to booming. While not all warrant emergency repairs, they can all signal an issue with your heating equipment.

If your furnace is making a terrible racket, know that we here at Technical Hot & Cold can come to your rescue. Schedule service today so we can help bring back some peace and quiet to your home.