6 Common Furnace Smells Explained

October 01, 2021

If your furnace smells while heating, it’s trying 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 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 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 created 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 641-812-2028 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 leak into your home. This colorless gas is fatal in large doses. So, it’s important to have an HVAC professional do routine 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, like 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, turn it off. If you know where your main gas supply valve is, turn that off too. Then contact the gas company and us for assistance.

4. Furnace Smells Like Sewer

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 very 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 contact 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 uses air ducts to distribute warm air across your house. Mold can grow in the ductwork over time, especially 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 on your own is difficult. Your comfort is our top goal at Kapaun & Brown Inc., so our professionals are here to help you when you need us. When you need furnace repair in Marshalltown that you can depend on, call us at 641-812-2028.