6 Common Furnace Smells Explained


If your furnace smells while heating, it’s attempting to tell you something’s up. 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:

  • Burning smell from the furnace
  • The furnace smells like burning plastic
  • A gas smell from the furnace
  • The furnace smells like sewer
  • Furnace smells musty
  1. Burning Smell from Furnace
    Cause: Dusty Furnace
    If your furnace smells like burning, it’s probably happening 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 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 issue. 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 (832) 501-3419 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 home. This colorless gas is fatal in heavy concentrations. 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 the 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 give off a small amount of gas when it turns on, 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 regularly.

    Cause: Gas Leak
    If your furnace smells like gas continuously, shut it down. If you know where your main gas supply valve is, turn that off too. Then call the gas company and us for assistance.

  4. Furnace Smells Like Sewer
    If your furnace smells like a 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 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 across your house. 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.

    Depend on Us for Your Furnace Repair Needs
    Trying to fix your heating and cooling system on your own is hard. Your comfort is our number one goal at Air Houston Mechanical LLC, so our pros are here to help you when you need us. When you need furnace repair in Huffman that you can depend on, call us at (832) 501-3419.

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