If your furnace smells while heating, it’s attempting to tell you something’s up. We’ve put together a list of the top six furnace smells so you can learn what causes them and how to repair 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 probably 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, resulting in the burning dust smell from your furnace.

2. Furnace Smells Like Burnt Rubber or 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 created 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 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 gets rid of carbon monoxide that’s naturally produced 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 routine furnace maintenance and have functional 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, like formaldehyde
  • Water around your furnace, as long as the condensate drain isn’t plugged
  • Flu-like symptoms

3. The Furnace Smells Like Gas or Rotten Eggs

It’s normal for your heating system to give off a little bit 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. The Furnace Smells Like Sewage

If your furnace smells like sewer, or rotten eggs, you’ll want to ensure you aren’t dealing with 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 pouring some water down the floor drain in your basement. If that doesn’t fix the problem, you might have a sewer leak, so you’ll want to call a company that does sewer line repair.

5. Furnace Smells Musty

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

Cause: Dirty Ductwork

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

Trust Us with Your Furnace Repair Needs

Trying to fix your heating and cooling system by yourself is difficult. Your comfort is our number one priority at Jack's Heating, Cooling, Stoves & Fireplaces, so our professionals are here to help you when you need us. When you need furnace repair in that you can depend on, call us at .