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6 Common Furnace Smells Explained

October 01, 2021

If your furnace smells while heating, it’s trying to tell you something’s wrong. We’ve compiled 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 house, your furnace accumulates dust over time. This dust burns off 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 problem. This smell of burning can be caused by melting plastic wire casing, which is a safety hazard. If you’re noticing a melted plastic smell, turn off your heating system right away and call us at 815-410-1231 for furnace repair.

Cause: Overheated Motor or Cracked Furnace Exchanger

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

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

Other signs 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 around your furnace, as long as the condensate drain isn’t blocked
  • Flu-like symptoms

3. Gas Smell from Furnace

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

Cause: Gas Leak

If your furnace smells like gas frequently, 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 make sure you aren’t dealing with a gas leak. If you don’t, the problem could be with your sewer lines and not your furnace. This is especially true if it’s been very dry lately.

Cause: Dry Sewer Trap or Sewer Leak

If you suspect your sewer trap is dry, you can try putting some water down the floor drain in your basement. If that doesn’t fix the issue, you might have a sewer leak, so you’ll want to contact a company that does sewer line repair.

5. Furnace Smells Musty

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

Cause: Dirty Ductwork

Your furnace uses air ducts to distribute warm air throughout your home. Mold can grow in the ductwork over time, particularly if you live in a humid climate. You can eliminate the mold by having an HVAC technician do air duct cleaning.

Trust Us with Your Furnace Repair Needs

Troubleshooting your heating and cooling system by yourself is difficult. Your comfort is our top priority at PWA Heating & Cooling Inc, so our professionals are here to help you when you need us. When you need furnace repair in Plainfield that you can depend on, call us at 815-410-1231.