Furnace Smells Like Burning When You Turn It On? What's Normal in LA
Los Angeles heating season is short, which means a lot of furnaces sit unused for months. Then the first cool evening arrives, you flip the thermostat, and the house fills with a smell like something is burning. It is alarming, and it is one of the most common heating questions we hear each fall.
Most of the time it is harmless. Sometimes it is not. Here is how to tell the difference, and what to do in each case.
The 3-minute version 1. A faint dusty, burning smell on the first startup of the season is normal and should fade within a few hours. 2. Rotten eggs or sulfur means leave the house and call SoCalGas at 1-800-427-2200. Plastic, rubber, electrical or chemical smells mean shut the heat off. 3. A smell that lingers past a few hours, or a heater that behaves oddly, is worth a professional look before you run it all winter.
1. Why your furnace smells the first time you turn it on
While the furnace is off, a fine layer of dust settles on the heat exchanger, burners and inside the ducts. When the system fires up, that dust burns off and gives you a hot, dusty, slightly smoky smell. It should start to fade within a few hours of running.
Older Los Angeles homes with gravity furnaces, the big floor furnaces with many large ducts, often hold even more dust, so the first-day smell can be stronger. If you have one, our gravity heating services page explains how we repair, service and replace them.
Run it with the windows open a crack: fresh air clears the dust smell faster.
Change the filter first: a clogged filter makes the smell worse and strains the system.
Vacuum nearby vents and registers: less dust in the path means less to burn off.
2. Smells that are not normal
Different smells point to different problems. Pay attention to what it actually smells like:
Rotten eggs or sulfur: natural gas has an added odor so you can detect leaks. Treat it as an emergency.
Hot plastic or rubber: often a foreign object in the ductwork or near a heater. Turn the heat off.
Electrical, gunpowder or metallic: can mean a failing wire or overheating motor. Shut the unit off.
Chemical odors: can point to a damaged heat exchanger, which should be inspected right away.
Musty or moldy: if it continues after a new filter, the ducts or drain pan may need attention.
A smell that comes from only one vent usually means something is stuck in that run of ductwork. A smell that is still strong after several hours of running is also a reason to call.
3. If you smell gas, do this right now
Gas smell: leave first, call second. Do not flip switches, use a lighter, or search for the source. Walk outside immediately, then call SoCalGas at 1-800-427-2200 from a safe place. Call 911 if anyone is in danger or you cannot reach the gas company.
Once the gas company has made the area safe, we can pinpoint the source. See our gas leak detection services and read our guide to the warning signs of a gas line problem.
4. A quick first-startup routine
Replace or check the air filter.
Clear anything stored near the furnace: boxes, paint, cleaners and anything flammable.
Turn the thermostat to heat and set it a few degrees above room temperature.
Stay nearby for the first 15 to 30 minutes and use your nose.
If the smell is fading after a few hours, you are likely fine. If not, shut it off and call.
The same goes for your water heater: if you notice its pilot light going out or acting up this time of year, see our guide to common water heater pilot light issues.
5. Check your carbon monoxide alarms before the heat runs all winter
A burning smell is not how carbon monoxide shows up, because CO has no smell at all. That is why the alarm matters. CO alarms belong on every level of the home and outside sleeping areas, with the batteries replaced once a year and the alarm tested monthly. Do this the same day you first turn on the heat.
Want your heating checked before the cold arrives?
If your furnace smell has not faded, or you would simply rather have a professional look at it, call Boss Plumbing at (323) 464-4700 or contact us online. We provide plumbing and heating service across Los Angeles.
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