6 Common Furnace Smells Explained

October 01, 2021

If your furnace smells while running, it’s trying to tell you something’s wrong. We’ve compiled a list of the top six furnace smells so you can learn 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 happening when you turn on your furnace for the first time in the fall. Like anything else in your house, your furnace gets dusty over time. This dust burns up when you turn on the heat, resulting in 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 601-292-9763 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 exhausts carbon monoxide that’s naturally created during the combustion process.

If it cracks, carbon monoxide can leak into your home. This invisible gas is fatal in heavy concentrations. 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, 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 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 regular basis.

Cause: Gas Leak

If your furnace smells like gas frequently, turn it off. If you know where your main gas supply valve is, shut that off too. Then call 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 make sure 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 suspect your sewer trap is dry, you can try pouring 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 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 send warm air across your house. Mold can grow in the ductwork as time goes on, 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 on your own is hard. Your comfort is our number one priority at Oak Grove Heating & Air Conditioning, so our professionals are here to help you when you need us. When you need furnace repair in Hattiesburg that you can depend on, contact us at 601-292-9763.