What You’ll Learn
Why is my furnace making a weird noise?
There are many reasons why your furnace might make noise, and it’s important to determine what type of noise it is to figure out what’s wrong.
Rapid clicking correlates to ignition troubles, hissing points to a dangerous gas leak, screeching signals failing bearings, booming is a warning of delayed ignition, and rattling relates to loose parts.
For any problem regarding strange noises, it’s best to call a professional.
In this post:
Henry couldn’t stand the on-and-off squealing of his furnace.
He’d been trying to ignore it for weeks, but last night was his final straw.
One bearing replacement later, and Henry found out he had been mere days away from losing heat completely.
Don’t ignore your furnace’s cries for help unless you want to risk spending a night with frozen toes.
Rapid Clicking: The Sound of a Stalled Start
If your furnace sounds like a repetitive ticking clock or a rapid-fire clicking when it tries to start up, it’s usually a sign of ignition trouble.
Think of this like a car that won’t turn over. Your furnace is trying to create a flame to heat your home, but something is standing in the way.
This is often caused by a dirty flame sensor, a failing igniter, or an issue with the gas valve.
When the system can’t verify that a flame has been lit, it clicks as it tries the sequence over and over again.
What You Can Do
Before calling in the pros, check your air filter.
It sounds simple, but a severely clogged filter can restrict airflow so much that the system’s safety sensors trip, causing it to struggle during the startup phase.
If a filter swap doesn’t silence the clicking, it’s time to call a technician.
Working with gas valves and sensitive igniters requires professional tools and calibration to ensure the unit remains efficient and safe.
Hissing: A Sound That Demands Action
Hissing is perhaps the most serious sound a furnace can make, and it should never be ignored. The hissing sound comes from gas leaking out of your furnace.
There are two primary culprits for a hissing sound, and both require immediate attention.
- Gas leak: Propane and natural gas are naturally odorless, but an additive that smells like rotten eggs is included for your safety.
- Cracked heat exchanger: This is the component that keeps the combustion gases (like carbon monoxide) separate from the air being blown through your vents. A crack is a major safety hazard.
What You Can Do
This is a matter of safety.
If you smell rotten eggs or sulfur along with the hissing, evacuate everyone from the home immediately and call 911 or your gas provider from outside.
If there is no smell, but the hissing is persistent, shut the furnace off at the power switch or breaker. It could be a significant duct leak or a cracked heat exchanger.
In either case, a professional inspection is the only way to ensure your family isn’t being exposed to carbon monoxide.
Screeching or Squealing: The Cry of Metal on Metal
A high-pitched screeching sound is hard to ignore, and for good reason. This sound almost always points to bad motor bearings or a failing blower belt.
Imagine a wheel on a wagon that hasn’t been oiled in years. Eventually, the friction becomes so intense that the metal begins to scream.
In your furnace, the blower motor is responsible for moving heated air throughout your 1,500+ sq. ft. home. When those bearings wear out, the friction creates heat and noise, eventually leading to a total motor seizure.
What You Can Do
There isn’t a “home remedy” for failing bearings.
This is a mechanical failure that requires the motor to be lubricated (if it’s an older model with oil ports) or, more likely, replaced.
Continuing to run a screeching furnace can cause the motor to burn out entirely, potentially damaging other electrical components in the process.
Call a pro to address this before the heat goes out completely on a sub-zero night.
Booming or Thumping: The “Delayed Ignition” Warning
Few things are more startling than a loud boom coming from the basement or utility closet.
This sound usually occurs right as the furnace starts a cycle, and it is the classic sign of delayed ignition.
What’s happening? Dust and dirt build up on the burners over time. This prevents the gas from igniting immediately.
Instead, gas builds up inside the combustion chamber for a few extra seconds before finally catching the spark. When it finally ignites, that extra gas creates a small, controlled explosion—the “boom” you hear.
Note: This mainly applies to older furnaces. Most modern furnaces are equipped with safety controls to prevent gas buildup, but do not ignore a booming noise, even if you have a new furnace.
What You Can Do
Turn the furnace off immediately.
This isn’t just a noisy nuisance; the physical shock of those mini-explosions can actually crack your heat exchanger over time. A cracked heat exchanger, as mentioned before, is a direct path for carbon monoxide to enter your living space.
This is a situation where professional cleaning and burner adjustment are required to keep the system running safely.
Rattling: The Shaking of the System
A rattle can be anything from a minor annoyance to a sign of internal fatigue.
Most often, it’s caused by loose panels on the exterior of the furnace or a vibrating blower wheel. As the furnace runs, the natural vibration of the motor causes anything not bolted down tightly to shake against the frame.
What You Can Do
This is one of the few sounds where you can take the lead.
Grab a screwdriver and check the exterior panels of your furnace. Often, a screw has vibrated loose over the years.
If tightening the panels doesn’t stop the noise, the rattle might be coming from the blower wheel itself (which may be out of balance) or a failing motor mount.
If the “quick fix” doesn’t work, have a technician look inside to ensure a small rattle doesn’t turn into a large, expensive break.
Don’t Ignore The Warning Sounds
Ignoring a strange sound might save a few dollars today, but it opens you up to more expensive issues later.
To have a better chance of avoiding the sounds altogether, get your annual furnace inspection done with Kauffman Gas.
Our priority is keeping your family warm and safe every day.
Contact Kauffman Gas today.
FAQs
Why is my furnace making a loud clicking sound but not turning on?
A rapid clicking sound usually indicates an ignition failure.
This often happens when a dirty flame sensor, a faulty igniter, or a malfunctioning gas valve prevents the burner from lighting. First, try replacing your air filter to ensure proper airflow.
If the clicking persists, contact a professional to inspect the ignition sequence, as handling gas components requires specialized tools and safety expertise.
Is a hissing noise from my furnace dangerous?
Yes, a hissing noise can be a serious safety concern. It often signifies a gas leak or a cracked heat exchanger, which can release carbon monoxide into your home.
If you also smell rotten eggs, evacuate immediately and call 911. If there is no odor, shut off the system and have a technician inspect your unit and ductwork to prevent hazardous air quality issues.
What causes a furnace to make a loud “boom” when it starts?
A loud “boom” or “thud” is typically caused by delayed ignition.
When dirt or soot builds up on the burners, gas doesn’t ignite immediately; instead, it accumulates and creates a small explosion when it finally catches.
This physical shock can eventually crack your heat exchanger. You should turn off your furnace and schedule a professional cleaning to prevent permanent system damage or carbon monoxide leaks.
How do I stop my furnace from making a rattling or vibrating noise?
Most rattling is caused by loose exterior panels or a vibrating blower wheel.
Start by tightening any loose screws on the furnace cabinet to see if the noise stops. If the rattling continues, it may indicate a detached blower fan or a failing motor mount.
A professional technician can balance the internal components and ensure that a minor vibration doesn’t lead to a major mechanical failure.