Key Takeaways
- A loud bang at start-up often means delayed ignition and should be checked promptly.
- Squealing and grinding usually point to blower motor or bearing problems.
- Rattling can be loose panels or something more serious, like a damaged heat exchanger.
- Any noise combined with a gas smell or a CO alarm is an emergency: leave and call from outside.
Is your furnace making noise it never made before? Most furnaces have a familiar soundtrack: a click, a soft whoosh as the burners light, and the steady hum of the blower. When that soundtrack changes, your furnace is usually trying to tell you something. In Ottawa, where heating systems run almost nonstop from late fall to early spring, small problems can grow quickly once temperatures drop below −25 °C.
This guide walks through the most common furnace noises, what they usually mean, what you can safely check yourself, and when it is time to call a professional.
Why Is My Furnace Making Noise All of a Sudden?
New noises usually come from one of four areas: the ignition and burners, the blower assembly, the ductwork, or the cabinet and venting. Some sounds are simple wear and tear. Others point to safety issues that should not wait.
Before you try to diagnose anything, keep this rule in mind: homeowners can change filters and check thermostat settings, but in Ontario any work involving gas valves, burners, venting or internal gas components must be done by a TSSA-licensed gas technician.
A quick note on normal sounds
Not every sound is a problem. A soft click when the thermostat calls for heat, a quiet whoosh when the burners ignite, a gentle hum from the blower and some light ticking as ducts expand and contract are all normal. It is the loud, new or changing sounds that deserve attention.
Common Furnace Noises and What They Mean
Banging or booming at start-up
A loud bang right as the furnace starts is often caused by delayed ignition. Gas builds up in the combustion chamber for a moment before it lights, causing a small burst. Dirty burners, a weak igniter or incorrect gas pressure are common causes. Over time, repeated delayed ignition can stress the heat exchanger. This is not something to ignore. Turn the furnace off at the thermostat and book a technician.
A softer popping or banging inside the walls or ceilings as the system heats up and cools down is usually duct expansion. Metal ducts flex as temperatures change. It is often harmless, though very loud duct noise can point to undersized ducts or restricted airflow.
Squealing or screeching
High-pitched squealing usually comes from the blower assembly. In older furnaces with belt-driven blowers, a worn or loose belt is a common culprit. In newer units, squealing often means the blower motor bearings are failing or need attention. Left alone, a failing motor can stop working entirely, usually on the coldest night of the year.
Grinding or scraping
A metal-on-metal grinding sound is more serious. It often means motor bearings are worn out or the blower wheel has come loose and is rubbing against its housing. Shut the furnace off and call for service to avoid further damage.
Rattling
Rattling can range from minor to serious. Loose access panels, screws or duct connections are common and easy to fix. However, rattling can also come from a loose blower wheel or, in some cases, a cracked heat exchanger. Because a cracked heat exchanger can allow carbon monoxide into the home, any persistent rattling should be inspected by a professional.
Humming or buzzing
A low hum while the blower runs is normal. A loud buzz, especially if the blower does not start, can point to a failing capacitor, a motor problem or an electrical issue. Electrical problems inside the furnace should always be handled by a qualified technician.
Clicking that does not stop
A single click at start-up is normal. Repeated clicking without the burners lighting often means an ignition problem, such as a worn hot surface igniter or a dirty flame sensor. Many furnaces will try several times and then go into lockout, leaving you without heat.
Whistling
Whistling usually means an airflow restriction. A clogged filter is the most common cause, but closed or blocked registers, undersized return ducts or air leaks around the filter slot can also be responsible. Restricted airflow makes your furnace work harder and can lead to overheating.
Gurgling or dripping
High-efficiency furnaces produce condensate water that drains away through a small pipe and trap. Gurgling or dripping can mean a clogged condensate line or trap. In Ottawa, condensate lines that run near cold exterior walls can also freeze in deep cold snaps, which may cause the furnace to shut down.
Get a Free Quote From Certified Ottawa Technicians
Upfront pricing • No hidden fees • Certified technicians
What You Can Safely Check Before Calling a Pro
- Replace the filter. A dirty filter causes whistling and strain on the blower.
- Open all supply registers and make sure furniture is not blocking returns.
- Check the thermostat settings and batteries.
- Clear outdoor vents of snow and ice after a storm, which is especially important for side-wall vents in Kanata, Barrhaven and Orleans subdivisions.
- Listen for where the sound comes from: the furnace cabinet, the ducts, or outside at the vent.
Do not remove internal panels, adjust gas components, or repeatedly reset a furnace that keeps shutting down.
When a Furnace Making Noise Becomes an Emergency
Some situations call for immediate action rather than a routine booking:
- You smell gas (a rotten-egg odour): leave the home right away and call the Enbridge Gas emergency line or 911 from outside.
- Your carbon monoxide alarm sounds: get everyone out and call 911 from outside.
- You hear loud bangs combined with a burning smell or visible smoke.
- The furnace stops working during extreme cold and pipes or vulnerable family members are at risk.
If your furnace has stopped heating and there is no gas smell or CO alarm, call KAD Mechanical & HVAC at (613) 790-2675 to book a furnace repair visit anywhere in Ottawa, Kanata, Nepean, Barrhaven and Orleans.
Repair or Replace a Noisy Furnace?
Many noises are fixed with a straightforward repair: a new belt, motor, igniter, capacitor or a thorough burner cleaning. Our furnace repair technicians will diagnose the cause and explain your options before any work begins.
If your furnace is older, needs frequent repairs, or the noise turns out to be caused by a cracked heat exchanger, replacement may be the more sensible choice. Older homes in neighbourhoods like Westboro and Alta Vista often still have original or second-generation equipment that is near the end of its life. A properly sized new furnace usually runs more quietly and can help lower Enbridge Gas bills. See our furnace installation options for more details.
Preventing Noises Before They Start
The best way to keep your furnace quiet is regular maintenance. An annual tune-up lets a technician clean burners, inspect the blower and motor, tighten electrical connections, check the heat exchanger and catch worn parts before they fail. Book furnace and water heater maintenance in early fall so your system is ready before the first deep freeze.
Costs for repairs vary with the part, the age of the furnace and how accessible it is. KAD Mechanical & HVAC provides upfront pricing with no hidden fees, and you can request a free quote anytime.
Talk to a Certified Technician Today
Call (613) 790-2675 or request your free quote online — we respond fast.
Frequently Asked Questions
Is it safe to run my furnace if it is making a loud noise?
It depends on the sound. Light ticking from ducts is usually harmless, but banging at ignition, grinding, or persistent rattling should be checked before you keep using the furnace. If you smell gas or your CO alarm sounds, leave the home and call from outside.
Why does my furnace bang when it turns on?
A loud bang at start-up is often delayed ignition, where gas builds up briefly before lighting. It is commonly caused by dirty burners or ignition problems and should be inspected by a TSSA-licensed technician.
Why is my furnace squealing?
Squealing usually comes from the blower assembly, such as a worn belt on older furnaces or failing motor bearings on newer models. Getting it repaired early helps avoid a complete breakdown.
Can a dirty filter make my furnace noisy?
Yes. A clogged filter restricts airflow, which can cause whistling and make the blower work harder. Changing the filter is one of the easiest things homeowners can do to reduce noise.
Certified, TSSA-licensed heating, water heater and gas technicians serving Ottawa, Kanata, Nepean, Barrhaven and Orleans for 10+ years.
Next article: Furnace Stopped Working in Winter? What Ottawa Homeowners Should Do
