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What Strange Furnace Smells Might Be Telling You

girl-pinching-noseWhen a furnace first turns on for the winter season, it emits a burning odor into the air from the vents. This is normal. It’s odor of the dust along the heat exchanger or heating elements burning off as the unit heats up. The smell will subside after a short time and the furnace will get into the regular groove of warming the house.

But if a furnace starts to smell funny after it’s started up for the season, it’s often a warning something is wrong that needs attention. We want you to know what these unusual odors may mean and when to call for furnace repair in Plattsburgh, NY from our team, so we’ve written a short guide. If you have any doubts about your furnace, don’t spend long analyzing it—shut the furnace off and call for assistance. Always better to be safe when it comes to a central furnace.

Rotten Egg Smell

We put this one first because it’s potentially the most harmful. A gas furnace with a cracked heat exchanger or leaking gas line can send toxic gases into a home. Because natural gas and carbon monoxide (a byproduct of natural gas combustion) are odorless and colorless, natural gas producers add a chemical called mercaptan that creates a noticeable “rotten egg” smell, similar to sulfur, to help people recognize CO and gas leaks. If you notice the smell or CO detectors in your house go off, leave the building immediately and call the gas company. Later you can contact our technicians to see what needs to be repaired.

Electrical Burning

You’re probably familiar with the smell of electrical wires burning—it’s a sharp, acrid odor. When you notice it coming from the furnace, it often indicates a motor burning out or loose wires on the control board. This also happens with a gas furnace, which uses motors and electrical parts along with gas burners. Shut off the furnace and call technicians.


The musty, dirty-sock smell of mold is one of the most unpleasant you may encounter wafting around your house. During the summer, the smell often indicates mold on the AC’s evaporator coil. When the furnace is running, the source may be a clogged air filter. The collection of lint and dust in a clogged filter is a perfect environment for mold to start to grow, especially with high moisture levels indoors. If the furnace has a permanent filter, the mold may have been growing for along time. (We don’t recommend permanent filters because of this.) Change the filter for a new one to see if this gets rid of the smell.


A general dusty odor from the furnace is usually because of lack of maintenance and cleaning. If you aren’t scheduling fall maintenance for the heating system each year, you may end up with a dusty furnace. Another source is ducts with dust buildup, which can occur after a few years without professional duct cleaning. The odor is usually a reminder that you need to schedule routine services to help the furnace perform its best.

Red Rock Mechanical, LLC serves Northwest Vermont & Northeast New York. Call us for furnace repairs—we offer emergency service!

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