Why Does My Furnace Smell?

All furnaces produce a number of strange odors.

Furnaces burn oil and gas or use electricity to heat your home all winter long. When you ignore the symptoms of serious furnace problems, the unit may malfunction and stop providing heat in the middle of a winter holiday celebration. Some odors and smells coming from your furnace indicate the need for repair or maintenance while others are safe to ignore.

Fuel Smells

Oil and natural gas-powered furnaces usually produce a very faint scent of burnt fuel, but you should never smell the strong odor of unburnt fuel, warns Preferred Home Repair. If the rotten egg smell of gas becomes strong enough for you to smell it in other rooms away from the furnace, you need to leave the house and call the fire department. This indicates a serious gas leak that could lead to an explosion. Leaking oil poses less of an immediate risk but will cause explosions inside the furnace, so oil odors should trigger a service call.

Musty Odors

When the damp, musty smell of mold or bacteria growth comes through the heating ducts, it may originate from the furnace or somewhere else in the basement or attic. The condenser pump that collects water from the furnace system needs annual cleaning. Water and dust collected in the pump breed bacteria and mildew, says Inspectapedia. If this is the cause, cleaning the pump will fix the problem. A musty smell that continues after the cleaning comes from somewhere else in the home.

Electrical Smell

Electrical odors smell like an overheated iron or hot metal, and in most cases, these smells coming from the furnace indicate broken or malfunctioning parts. All furnaces use a variety of electrical wiring and small motors to move air and start the combustion process. When these parts burn out, they release an electrical smell into the heating system, according to Hannabery HVAC Services. A dirty air filter increases the chances of electrical components overheating, but once they are broken, they'll need replacement.

Burning or Dusty Odors

Dust gathers in the combustion chamber, especially when the furnace doesn't run for many months. When the furnace starts up again, the dust burns off and releases a burning odor and small amounts of smoke. Dirty filters full of dust make the problem worse, says National Furnace Heating and Air Conditioning. New furnaces also produce burning odors as the oil used to keep the components from rusting burns off. If the smell continues beyond the first day of use, something else is burning inside the furnace, and you need to call a service technician to prevent further damage.

References

• Preferred Home Repair; Troubleshooting - Gas Furnace; Scott Clark
• Inspectapedia: Odors & Smells - How to Find and Remove Odors, Gases and Smells in Buildings
• Hannabery HVAC Service: Commonly Reported HVAC Problems - Odors
• National Furnace Heating and Air Conditioning; Furnace Safety and Maintenance Advice; David Carlson