7 Furnace Noises and Smells Explained

Furnace heating process

When everything is functioning properly, your furnace should make your home warm and cozy without making any odd sounds or smells. However, heating system malfunctions are common, and this winter, you may find yourself contacting a technician to investigate a strange furnace sound or odor.

Here is what your furnace is trying to tell you, based on the noises and smells it makes.


Below are three of the most common smells that technicians receive calls about.

1. Burning Smell

A burning odor does not always mean that something is wrong with your furnace’s equipment. If it smells like something is burning when you first turn your heating system on for the season, what you’re most likely smelling is the dust burning off. As long as the odor goes away within an hour, there’s no major cause for concern—however, you should consider getting your furnace professionally serviced to avoid ignition and efficiency issues caused by dust buildup.

If the burning smell doesn’t leave, or it smells specifically like burning rubber or plastic, you’ve got a problem. Before anything else, make sure your system has a clean air filter. A dirty air filter can block airflow into your furnace and cause the parts to overheat.

If replacing the air filter doesn’t help, you may have one of the following system issues:

  • Overheating electrical components have started to burn or melt.

  • A foreign object has fallen into your heating system and is starting to burn.

  • Your furnace needs a new oil filter (this only applies to oil-burning furnaces).

At this point, it’s best to involve a technician to help you diagnose and solve the problem.

2. Musty Smell

If the air from your heating system is smelling less than fresh, then you may have a problem with mold growth. The growth might be on one of your furnace’s components or in your ductwork.

Dusty conditions inside your heating system provide mold the food that needs to grow, while the condensation in your furnace gives mold the necessary moisture. It’s also possible for dust, mold, and humidity to enter your system through leaky air ducts. You’ll get the best long-term solution by contacting an HVAC contractor to figure out where the mold growth is happening in your system.

3. Rotten Egg, Sulfur-Like Smell

This odor means one thing: a natural gas leak. Gas leaks are considered an emergency because of how dangerous they are. If you can smell gas in your home, evacuate everyone immediately. Do not turn anything off or on and do not plug in or unplug anything on your way out. After you’re safely outside, call your gas company and inform them of the leak.

Any gas-related issues in your furnace should be handled by a licensed HVAC technican. Remember that natural gas is extremely flammable, so repairs should only be performed by trained professionals.


If you hear any of the sounds below coming from your furnace, it’s time to call a professional.

1. Metallic Scraping Noise

This sound usually indicates that your furnace’s blower wheel simply needs to be tightened. However, if you put off this repair, the malfunctioning blower wheel can cause further damage to your system.

2. Popping, Banging, or Knocking Sound

Keep an “ear out” for these sounds particularly when your furnace is starting up, as they could indicate an ignition or combustion problem. The occasional pop from your air ducts is normal, as heat will make them expand, and cooling off will make them contract.

3. Clunking Noise

If your furnace is making a heavy, dull, clunking sound, there could be an issue either with the bearings of the belt. Over time, these parts can suffer from wear and tear, and the belt can become cracked.

4. Shrill Whining or Screeching

If a motor bearing or belt problem becomes bad enough, it may progress from making clunking noises to an alarming screech. The bearings can usually be adjusted and fixed with some professional lubricant, but the belt will most likely need to be replaced.

Does your home need a furnace repair? Contact the Decatur heating experts at Jackson Plumbing, Heating & Cooling today: (256) 304-8883!