What Is That Burning Smell Coming From My Furnace?

The most common cause of a burning smell on the first cold day is dust that settled on the heat exchanger and burners over the summer and is now cooking off. That smell usually fades within a few hours. A smell that lingers, gets stronger, or comes with smoke, a rotten egg odor or a scorched electrical scent is a different matter, and the furnace should be turned off.

Below are the usual causes, how to tell them apart, and where a homeowner's role ends.

Dust burning off

After months of sitting idle, a furnace collects a layer of dust inside. When you fire it up in the fall, that dust burns off and smells like hot dust or toast. Tri-Cities homes see this more than most, since the dry climate and wind push fine dust through every gap.

Run the system for a while with a window cracked if the smell bothers you. If it clears and does not return, you are probably fine. A fresh filter helps, and a pre-season tune-up reduces the amount of dust waiting to burn.

Overheating parts

A sharper, hotter smell can mean components are running too warm. A dirty, clogged filter is the classic culprit because it restricts airflow and lets the furnace overheat. A failing blower motor, worn belt or bearing can produce a burning rubber or hot metal smell.

Check the filter first, since that is a safe, simple job. If the filter is fine and the smell continues, turn the furnace off at the thermostat and call a technician rather than running it and hoping.

Electrical smells

A scorched plastic or fishy electrical odor can point to a failing wire, capacitor or control board. Electrical faults can become fire hazards, so shut the system off at the breaker if you are able to do so safely, and leave repairs to a licensed professional.

The smell of gas

Natural gas has an added rotten egg odor so leaks are noticeable. If you smell it, do not turn lights or appliances on or off and do not use a phone inside. Get everyone out and call your gas provider or emergency services from a safe distance. This is never a do it yourself situation.

A related concern is carbon monoxide, which has no smell. Working carbon monoxide detectors on each level of the home and near sleeping areas are an important backup, and if one sounds, leave and call for help.

Quick guide

• Dusty smell for a few hours on the first run of the season: usually normal
• Burning smell with a dirty filter: replace the filter and watch whether it clears
• Hot rubber, metal or electrical smell: shut the furnace off and call a technician
• Gas or rotten egg smell: leave the home and call from outside

Prevent problems before winter

A yearly furnace tune-up clears dust, checks the burners and heat exchanger and tests the safety controls before you rely on the system daily. Changing your filter regularly does a great deal to keep airflow healthy.

One more possibility: not every burning smell starts inside the furnace. Paper, toys, laundry or stored items placed too close to the unit can scorch when the burners fire, and a spilled cleaning product on a warm surface can give off a sharp odor. If your furnace sits in a closet, garage or utility room, keep a clear area around it and never use the space to store anything flammable. Check that nothing has fallen into the return or slipped behind the unit, since even a small item can cook against a hot surface.

If a smell has you worried, Air-Tech is ready to look at it. The Pasco office is at (509) 392-2021, and there is 24-hour emergency service for the smells that cannot wait until morning.