If your furnace smells bad, it may be trying to tell you something.


Furnace smells bad? We nose what to do.

Ever notice that your furnace smells bad when you turn it on the first time? That nasty smell may be a bother if you’re expecting guests. But at the very least, it is a clear indicator of your furnace requiring maintenance — especially if it smells like burnt hair or dust. There are a few other odors that can indicate some further danger.

Here are a few reasons why your furnace stinks after turning on the heat:


If you haven’t gotten a regular furnace maintenance and cleaning, you will likely detect a musty, burning scent emanating from your vents. Back in college, I did this once and set off the smoke alarm. So, what causes your furnace to smell bad?

In a few words: Dust, pet dander, hair, and lint. While not directly harmful, it’s unpleasant and can be easily avoided with a furnace cleaning before winter. Your home comfort system circulates A LOT of air through the system — in both heating and air conditioning. With that air comes a lot of dirt that builds up in critical areas of the system.

Just imagine what’s in your vacuum cleaner bag. Add some water from the air conditioning system and… wallah, that’s the kind of yuck built up and caked on to the inner parts of your heating and cooling system. When you turn the furnace on at the beginning of the season, all that caked on nasty gunk is burning off and emanating those wretched odors into the air in your home. Don’t worry; the only danger is to the longevity and performance of the system.

The simple solution is a Service Legends WOW Tune-Up, which involves our Home Comfort Heroes getting in there and cleaning that system top to bottom in all the tight spots.


Does the air from your furnace smell, stale, musty, or somewhat dirty? This usually goes hand-in-hand with flaring allergies and irritable noses. A dirty filter, dusty ventilation ducts or an evaporator coil caked with a layer of gunk are typically to blame.

Replacing your furnace filter is a great first step. The filter itself needs to be replaced every 1 to 6 months, depending on the filter type and filtration system design. A more advanced next step would be to remove your vent and shine a light into the vent to see how dirty your air ducts are. We can help you with a full cleaning and resealing of your ductwork to keep your air healthy and smelling fresh.


What about burning plastic or smoke? These are far more serious furnace smells. They could be caused by an overworked motor heating up or flame rollout.

Have you noticed reduced airflow from your vents or electrical failure in or near the furnace? This odor requires an immediate response.

Turn off your furnace, take a look at the furnace itself while paying special attention to any blackening or charred areas behind the furnace door in the burner area and call for an emergency repair immediately. You’ll want your furnace back online soon, but a house fire is too warm for anyone.


This is more common for homes using propane-fueled heating systems (or have propane lines into the house for cooking or heating water). Propane and natural gas have no odor detectable to human senses. They are odorless and colorless, making them invisible to human perception. Since this gas is dangerous to humans, the powerful and very evident scent of rotten eggs is added to it.

If you pick up a whiff of this odor at any time in your home, leave the home immediately and then:

  • 1st – call the utility company and have them come safely shut the gas off to the entire home.
  • 2nd – call a residential heating contractor to ultimately correct the problem.

These are the most common reasons. Other reasons require more drastic cleaning measures as you’ll occasionally smell the scent of sewage from an open black water line or even decay from animals that have snuck into your ventilation system over the summer. This could be why your furnace smells bad and the unit needs to be fully serviced each fall before you turn on your system.


At Service Legends, we take pride in heating and cooling Des Moines and the surrounding areas — especially if your furnace smells bad. Our HVAC services include furnace and air conditioner installation, repairs, maintenance, and tune-ups. Our lineup of Indoor Air Quality solutions includes whole-home humidifiers, air purifiers, and air filtration systems. We can even help with HVAC financing.

515-657-6634Request Appointment Online