Furnace Noises Explained

Your furnace plays a critical role in keeping you warm all winter long. When properly maintained and working at peak efficiency, it transforms cold air into warm air to keep you cozy and comfortable. But as a furnace ages, it’s more likely to have worn or broken parts and to lose some of its efficiency. When this begins to happen, you may notice unusual sounds coming from the unit, ranging from clicking and popping to screeching and grinding.

While some of these noises are normal, others point to problems that need immediate attention. So, to prevent an untimely system breakdown , get to know the sounds your furnace should and shouldn’t be making so you can act accordingly.

What Noises are Normal?

It’s normal to hear a popping or clicking sound as your furnace starts up, especially if it’s an older unit. This is usually a sign that the furnace is igniting and working properly. However, the furnace should then settle into a dull hum as it kicks into gear.

Other common noises include:

  • A crackling sound as metal components cool after a heating cycle
  • A dull humming sound once your heater ignites
  • A pinging noise as metal comes into contact with your duct system
  • Banging and popping as ducts expand and contract

What Noises May Be Cause for Concern?

Now that you know which noises are common, here are some you shouldn’t ignore. If you notice any of the following sounds, contact a licensed HVAC technician right away to prevent damage to your heating system.

Loud Banging or Popping

While some banging and popping sounds are normal, if the sounds are exceptionally loud and frequent, they can signal a problem with your furnace like dirty burners that delay ignition. You may also experience a crack in the heat exchanger, which could lead to a carbon monoxide leak. Make sure CO detectors are installed on every level of your home, including the basement. If you suspect a leak, evacuate your home and call your local fire department from a safe location.


When an oil furnace “knocks”, it’s usually caused by air bubbles trapped in the lines. The solution is to “bleed the lines”, which involves draining the lines to remove the trapped air. This task should be performed by a licensed professional.


Grinding noises coming from the direction of your oil furnace are never good news, as they typically indicate a part has worn out and needs repair or replacement. When you hear grinding, shut down the furnace and contact an HVAC tech for a diagnosis.


A scraping noise may mean the blower wheel has come loose or is broken and needs replacement. Turn your furnace off immediately and call a technician to inspect it. Left unattended, it can lead to considerable wear and tear on your system and cause more costly damage.

Humming or Buzzing

Many furnaces produce a dull humming sound while running. However, if you notice a loud humming or buzzing sound, there could be an issue with the motor or the fan. While it also may be something as simple as a loose screw, loose door, or improperly installed furnace filter, it’s best to have a professional check it out.


A rattling sound could indicate that a part has come loose internally. In rare cases, rattling could also mean there’s a crack in your heat exchanger. A malfunctioning heat exchanger can leak carbon monoxide into your home, putting you and your loved ones at risk. If your carbon monoxide detector is going off or if you suspect a carbon monoxide leak, leave the house and call the fire department from a safe location.

Screeching or Squealing

Screeching, squealing, or whining can indicate a belt has been stripped or has slipped out of place, or a problem with the blower motor. In some cases, the issue can be resolved by adjusting the tension of the belt. However, a worn-out or damaged belt or a problem with the lower motor will need the expertise of a professional.


If a clicking sound persists throughout the heating cycle, it often means there’s a problem with the ignition system. If your furnace can’t ignite, it may produce a clicking sound as the igniter struggles to come on. It’s best to contact a professional technician to inspect your furnace if it makes repeated clicking sounds.

When to Contact an HVAC Expert

In some cases, furnace noises are a sign of normal operation. But many of these noises can result in serious safety issues, such as carbon monoxide leaks, or broken parts that prevent the system from heating your home properly. If your heating equipment is making any noise in excess, or you just aren’t sure what the noise means, contact Air Professional Associates right away. Our team of home comfort experts are equipped with the knowledge and tools to diagnose and repair a variety of furnace problems. And if system replacement is needed – well, we can help with that, too. 

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