6 Furnace Odors and Their Possible Causes

The temperatures for Northern Texas are headed in the 40-degree territory, and furnaces across the Dallas–Fort Worth region will warm hands and hearths once again.

Some furnace smells are normal after you turn your furnace on after its long summer rest. Other furnace smells are signs of furnace trouble. When you turn on the heat this autumn, keep your nose alert for these six furnace odors.

1. Rotten Egg or Gas Smell

If your furnace operates with propane, natural gas, or LP gas, there may be a slight odor of gas as you open the fuel line to your furnace for the first time. If the gassy or rotten-egg odor lingers, shut off both your gas supply and your furnace right away.

Remove people from any rooms that have gas odors. Make sure your carbon monoxide detectors are working so you’ll know if the air is too dangerous to breathe in adjacent rooms.

If you're able to do so, check the connections and lines leading from your furnace to the gas fuel source. A fitting may have come loose, or a gas line may have been damaged and sprung a leak. If you can't find the source of the gas smell, call your gas provider or your HVAC repair service to isolate the leak.

In some cases, the gas smell problem requires only a simple adjustment. Your gas pilot light may not be lit properly, or the burners may need a good cleaning.

2. Dusty, Acrid Smells

It's normal for your furnace to smell a bit dusty when you first turn it on for the cold-weather season. During the spring and summer, dust blows around inside the furnace and settles on various components.

When the furnace is fired up for the first time in a long time, the dust particles heat up and give off a slight burning smell. As long as no smoke is coming out of the furnace — and the dusty burning smell goes away after a short time — the acrid smell is harmless.

3. Sharp Mildew and Mold Smells

Like dust, mold and mildew can collect on unused furnace components. A small amount of mold or mildew may dissipate on its own after a few cycles of the heating unit. If you smell a strong mold or mildew odor, the mildew or mold is entrenched. Your furnace needs a deep clean.

A cleaning solution like bleach may be necessary to remove the mold and mildew from furnace parts. You can clean your furnace yourself, but you need to shut off the power to the appliance and be very careful around some of the furnace components.

You should wear a mask and gloves when cleaning the furnace, and be extremely careful with any liquids around wires, switches, outlets, and other sensitive components. Let your HVAC professional tackle the furnace-cleaning job if you aren't confident about working around your furnace.

4. Formaldehyde or Chemical Smells

If you smell a chemical odor coming from your ducts or your furnace, suspect a cracked heat exchanger. When a heat exchanger develops cracks or corroded spots, they allow gases from the furnace to mix with the blower-forced air.

Some people say a cracked heat exchanger emits an odor similar to the smell of formaldehyde. If you catch a whiff of this chemical odor when your heat is running, shut off your heat pump or furnace immediately.

Running a furnace or other heating unit with a cracked heat exchanger is dangerous for everyone in your household. Around 1,500 people die in the U.S. each year because they're exposed to broken heat exchangers that spew out toxic gas.

Call your HVAC professional to replace your heat exchanger as soon as possible. You can't tell if your heat exchanger is compromised by looks and smell alone. Your HVAC expert will conduct tests of your furnace to make sure that's where the chemical smell originates.

5. Metal, Plastic, or Rubber Smells

Your furnace is made up of a wide variety of interconnected parts. Any one of those components can overheat and cause a burning smell.

Do you notice a hot plastic smell? An electrical short, wire damage, or an incomplete wiring connection could be causing the burning smell. Wires may have fallen out of place and into contact with a hot part of the furnace.

A metallic or rubber smell can indicate that a blower motor, belt, or other mechanical part is worn. A wobbly fan may scrape and leave a faint metallic or singed-wire smell.

6. Smoke and Visible Fumes

Whenever you see smoke or visible fumes coming out of your furnace, shut off the power to the HVAC system immediately. Contact your HVAC repair specialist as soon as possible.

A serious furnace fire can result from a number of factors, but smoke from the furnace can also be caused by less dire situations. A small bit of debris or a rubber component may be smoking but not actually on fire. The only way to know for sure is to call in the experts.

If your furnace smells weird or like it's burning, contact Henry's Service All today to schedule a complete inspection of your HVAC system. We diagnose and repair strange smells in furnaces throughout the Irving and Dallas-Fort Worth areas.