Sometimes your furnace can produce odors. But how do you know which furnace smells are harmless and which need immediate HVAC service? Here are five of the most common odors you may encounter and what each one means.

Burnt Dust

This one you might be familiar with at the beginning of furnace season. While it’s a little alarming to smell something coming from your vents, it’s nothing to be alarmed about. While not in use, dust gathers on the furnace parts and when the furnace turns on and those parts heat up, a slight burning smell can fill your home. After a heat cycle or two, the odor should clear up on its own as the dust burns away completely. If you want to minimize the odor in the future, dust your furnace before turning it on.


If you notice a musty smell, it could be cause for concern. Musty odors are created in dark, damp environments, and could mean there’s potential damage. As the moisture builds up, it can lead to mold and mildew growth. You should get your furnace checked, as well as your air ducts. Getting your ducts checked and cleaned will ensure they’re dry and odor-free.

Burning Rubber or Plastic

If you notice your furnace smells like burning plastic, that usually indicates the damage or failure of a plastic component. This can mean parts or electrical elements inside your furnace are getting too hot. In this case, it can smell like hot plastic, rubber, or burning oil. If you notice any smells similar to those, shut off the furnace as soon as you can and call a technician.


This smell may be a little harder to pinpoint, but you’ll know it when you smell it. Electrical wiring inside your furnace can create a distinct metallic odor as it burns. Electrical shorts caused by damaged or unshielded wiring can create sparks and melt wiring insulators. Furnace parts made entirely of metal can also give off strange metallic odors as they overheat. Just like in the case of a burning plastic smell, if you smell metallic odors coming from your furnace, shut the unit down and have a technician see if there are any issues that could cause overheating.

Rotten Eggs

If you smell rotten eggs after you’ve started your furnace, then you’ve come across some bad news. Natural gas and propane are odorless and colorless in their natural state, and this makes it nearly impossible to detect them. Because of this, methyl mercaptan is added to natural gas and propane. This colorless chemical compound has a smell similar to rotten eggs or cabbage, so it makes finding natural gas and propane easy.

If you smell rotten eggs, that means there’s a gas leak. If you believe it’s coming from your furnace, shut it down immediately and leave your home. Once you’re outside, call the local gas company or fire department to shut off your home’s gas supply and trace the source of the leak. If it turns out your furnace is the reason behind the gas leak, an HVAC technician can help repair or replace your unit.

 Comfort World Air Conditioning & Heating is Here for You

No matter what furnace smells occur, you can count on our HVAC professionals to sniff them out and fix them! We’ve been bringing comfort to the valley for over 30 years, so you can count on us to get the job done right. Our highly trained technicians in Scottsdale, Arizona, want to bring a little more comfort to your world!