Every furnace makes some noise: a click when the thermostat calls for heat, a soft whoosh when the burners light, the hum of the blower. What matters is a new sound, or one that's getting louder. Here's what the most common furnace noises usually mean, which ones you can check yourself, and which ones mean you should turn the furnace off and call.
Squealing or screeching
A high-pitched squeal usually comes from the blower. On older furnaces, a worn or loose belt is a common cause. On newer furnaces with a direct-drive blower, it often points to a motor bearing that's wearing out. It won't fix itself, and a failing blower motor can leave you without heat, so have it looked at soon.
Rattling
- Check the furnace door first: a panel that isn't seated properly can rattle every time the blower runs.
- Listen to the ductwork: loose duct connections or screws can rattle and tick as the metal heats up.
- Rattling from inside the furnace can be a loose part in the blower or inducer motor. That one is for a technician.
Clicking with no heat
A single click at startup is normal. Repeated clicking with no flame usually means an ignition problem: a worn igniter, a dirty flame sensor, or a gas valve that isn't opening. Many furnaces will try a few times and then lock out for safety. Check that the furnace switch is on and the filter isn't clogged, and if it keeps clicking, call for service.
Humming or buzzing
A low hum from the blower is normal. A loud buzz, especially one that comes with the blower not starting, can point to an electrical part such as a capacitor or a relay. Electrical problems inside the furnace should be handled by a technician.
A loud bang or boom when it starts
A bang when the burners light can mean gas is building up before it ignites, often because of dirty burners or an ignition delay. Don't ignore this one. Turn the furnace off at the thermostat and the switch, and call for service. If you ever smell gas, get everyone out and call your gas utility or 911 from outside.
Whistling
A whistle often means the furnace is struggling for air. Check for a clogged filter, closed or blocked vents, and return grilles covered by furniture. See how often to change your furnace filter.
How we help
Our NATE-certified technicians find the source of the noise and explain what's going on in plain English. We start with a $79 diagnostic, credited toward the repair if you go ahead, give you a written price before any work starts, and back every job with our 1-year parts and labor warranty. We offer same-day service and answer the phone 24/7.
Learn more about furnace service, read our furnace tune-up checklist, or see repair or replace your furnace.
- Why is my furnace squealing?
- Squealing usually comes from the blower: a worn or loose belt on older furnaces, or a motor bearing wearing out on newer ones. Have it checked before the motor fails.
- Is a loud bang from my furnace dangerous?
- It can be. A bang when the burners light can mean gas is building up before it ignites. Turn the furnace off and call for service, and if you smell gas, leave the house and call your gas utility or 911.
- Why does my furnace click but not turn on?
- Repeated clicking with no flame usually means an ignition problem, such as a worn igniter, a dirty flame sensor, or a gas valve that isn't opening.
- How much does a furnace diagnostic cost?
- Our diagnostic is $79, and it's credited toward the repair if you go ahead with the work.