6 Common Furnace Smells Explained

October 01, 2021

If your furnace smells while running, it’s trying to tell you something’s up. We’ve put together a list of the top six furnace smells so you can know what causes them and how to fix them. These include:

  1. Burning smell from furnace
  2. Furnace smells like burning plastic
  3. Gas smell from furnace
  4. Furnace smells like sewer
  5. Furnace smells musty

1. Burning Smell from Furnace

Cause: Dusty Furnace

If your furnace smells like burning, it’s likely occurring when you turn on your furnace for the first time in the fall. Like anything else in your home, your furnace accumulates dust over time. This dust burns up when you turn on the heat, causing the burning dust smell from your furnace.

2. Furnace Smells Like Burning Plastic

Cause: Electrical Problem

If your furnace smells like burning plastic or burning rubber, it might have an electrical issue. This smell of burning can be caused by melting plastic wire casing, which is a safety issue. If you’re noticing a melted plastic smell, turn off your heating system right away and call us at 636-206-4250 for furnace repair.

Cause: Overheated Motor or Cracked Furnace Exchanger

An electrical burning smell could also mean your furnace motor is too hot or the heat exchanger is cracked. The heat exchanger safely exhausts carbon monoxide that’s naturally created during the combustion process.

If it cracks, carbon monoxide can seep into your house. This colorless gas is fatal in large doses. So, it’s important to have an HVAC professional do annual furnace maintenance and have functional carbon monoxide detectors.

Other symptoms of a cracked heat exchanger include:

  • Soot on or inside the furnace
  • Yellow burner flame, instead of blue
  • Chemical smell from furnace, such as formaldehyde
  • Water near your furnace, as long as the condensate drain isn’t plugged
  • Flu-like symptoms

3. Gas Smell from Furnace

It’s normal for your heating system to give off a small amount of gas when it starts up, so you might notice a gas smell from your furnace. But it’s not typical to be smelling natural gas or rotten eggs throughout your home on a daily basis.

Cause: Gas Leak

If your furnace smells like gas continuously, shut it down. If you know where your main gas supply valve is, shut that off too. Then contact the gas company and us for help.

4. Furnace Smells Like Sewer

If your furnace smells like sewer, or rotten eggs, you’ll want to ensure you don’t have a gas leak. If you don’t, the issue could be with your sewer lines and not your furnace. This is especially true if it’s been extremely dry lately.

Cause: Dry Sewer Trap or Sewer Leak

If you think your sewer trap is dry, you can try putting some water down the floor drain in your basement. If that doesn’t solve the problem, you might have a sewer leak, so you’ll want to call a company that handles sewer line repair.

5. Furnace Smells Musty

If your furnace smells musty, mold and mildew has probably been growing in it for some time.

Cause: Dirty Ductwork

Your furnace works with air ducts to distribute warm air across your house. Mold can grow in the ductwork over time, particularly if you live in a humid climate. You can get rid of the mold by having an HVAC technician do air duct cleaning.

Depend on Us with Your Furnace Repair Needs

Trying to fix your heating and cooling system on your own is difficult. Your comfort is our top goal at Air Alliance Team, so our pros are here to help you when you need us. When you need furnace repair in Ballwin and St. Charles that you can trust, call us at 636-206-4250.