When you first turn on your home's furnace for the season, you may be accustomed to a slight smell when the dust that has settled within the system burns off. Usually, this odor will quickly dissipate.
However, if you detect a burning odor any other time that does not disappear after a couple of minutes, there could be a serious problem with the system. Below are a couple of possible reasons why your furnace is emitting the smell.
1. Smell of Metal Burning Indicates the Furnace's Electrical System Is Overheating
One possible reason why your furnace is giving off a burning odor that does not go away may have something to do with the electrical wiring of the system. There could be wires that have become frayed, or there may be an issue with power surges inside of the unit.
When the odor reminds you of metal burning, the wiring is most likely overheating. Usually, if there is too much power or heat inside of the system, the unit's safety switch mechanism will trigger and shut down the furnace.
However, if the switch is malfunctioning, the wires will stay hot and start to emit the odor you are detecting. The prudent thing for you to do is to discontinue running the furnace until a professional can assess the problem.
2. Odor Resembling Gunpowder Means the Blower Motor's Circuit Board Is Malfunctioning
Another possible reason why your furnace is producing a burning odor is that there is an issue with the blower motor's circuit board. Resembling the smell of gunpowder, the odor may be coming from the circuitry that is receiving too much electricity. Or, the circuits themselves may be causing shorts within the system.
Since the odor of a malfunctioning circuit board is distinctive, if you do detect the gunpowder smell, you need to switch off your furnace as soon as possible. If it continues to run, it will fry the circuit board, which will result in costly repairs or total replacement of the blower motor.
Unless you know that the odor is caused by dust burning off and the smell dissipates quickly, there could be a serious issue with the unit's electrical wiring or blower motor. Turn off the furnace to avoid further damage, and contact an HVAC contractor near you who offers furnace repair services to have them fully inspect the system and discuss with you what needs to be done to fix it.