Why does my furnace smell like burning when I first turn it on?

Where does that first burning smell come from?

Usually it is dust. Over the summer, dust settles on the burners and the heat exchanger, the metal chamber the flame heats. When the burners first light in the fall, that dust burns off. Carrier's furnace odor guide describes this, and Trane's troubleshooting page adds that dust in the ductwork burns off too.

In Northeast Ohio it usually shows up on the first cold night.

Which smells mean shut it off and call?

Burning plastic, rubber or hot wiring; a dust or new furnace smell that will not fade or keeps coming back; and a musty smell a new filter does not fix. Gas, smoke, a CO alarm or CO symptoms are different: touch nothing and get everyone out first.

How long should that first run smell last?

Minutes to a few hours, not days. Carrier says the burning dust odor typically lasts about 30 minutes to a few hours, and lists a smell that lasts longer, grows stronger or "returns repeatedly" as a reason to call.

A brand new furnace

A new furnace has its own first run smell. Trane blames special coatings and lubricants, says it can smell of burning dust, plastic or oil, and should fade in about an hour. If it lingers, turn the furnace off and call the installer.

What if it smells like burning plastic, rubber or hot wiring?

Turn the furnace off and call: that smell is not dust. Carrier says a burning plastic smell can come from an overheated blower motor, possibly from heavy dust buildup or a clogged filter, and an electrical smell can mean an overheating motor or damaged wiring. Trane says a melting plastic smell may be the casing on the furnace's wires, which it calls a big safety hazard. Lennox adds a milder cause: something that fell into a register over the summer. Treat burning rubber the same way, unless the furnace is brand new (see above).

Smoke or flames mean a fire: get everyone out, then call 911 from outside. In a fire, Ready.gov says, every second counts.

If there is no gas smell, no smoke and no flame:

1. Set the thermostat to Off.
2. Turn off the furnace power switch, which looks like a light switch on or near the unit.
3. Open windows or run exhaust fans. Carrier warns that burning plastic can give off toxic fumes.
4. Shine a flashlight into the floor registers and remove any toy or plastic item you can reach.
5. Do not switch it back on, even to test it. Carrier says to stop using it until a qualified HVAC professional has inspected it, and not to diagnose or repair electrical or combustion problems yourself.

What does a rotten egg or gas smell mean?

It can mean a natural gas leak. Leave the house now with everyone in it, and do not touch the furnace, the thermostat, a light switch or a phone on the way out. Enbridge Gas Ohio explains that mercaptan is added to natural gas so a leak smells like sulfur or rotten eggs; a hissing or whistling sound near the meter, pipes or appliances is another warning sign. Its instructions, in short:

• Leave doors and windows open behind you only if that does not slow you down.
• Do not smoke, and do not use phones, switches or electronics. Do not turn lights or appliances on or off, and do not start a car nearby.
• Do not look for the leak yourself.
• Once you are safely away, call Enbridge Gas Ohio's 24/7 emergency line at 1-877-542-2630, or 911.

If a different utility delivers your gas, call its emergency line or 911. Do not call a retail supplier you buy gas from through Energy Choice: Enbridge Gas Ohio says it still handles emergencies for customers who buy from a supplier. With propane heat, leave the same way and call 911 or your propane supplier from outside.

Carbon monoxide has no smell

Your nose will not warn you about carbon monoxide (CO), which Enbridge Gas Ohio says can come from a furnace that is malfunctioning or has blocked vents. The CDC calls CO odorless and colorless, lists its symptoms as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as flu like, and warns that people who are sleeping can die from it before they have symptoms. That is the job of a CO alarm, which Enbridge notes does not detect natural gas: the rotten egg smell is still your gas warning. Alarm or no alarm, if anyone has those symptoms while the furnace runs, especially if more than one person does or they ease outdoors, do what the U.S. Consumer Product Safety Commission says for suspected CO poisoning: get everyone outside to fresh air immediately, then call 911.

• The U.S. Consumer Product Safety Commission says CO alarms belong on each level of the home and outside sleeping areas, tested monthly, but not in attics or basements unless someone sleeps there.
• The CDC recommends checking batteries when the clocks change and replacing the detector as the manufacturer says or every 5 years.
• If a CO alarm sounds, Enbridge says to go outside immediately, call 911 from a safe location, and not go back in until a qualified professional, such as a firefighter, says it is safe.

Enbridge also says to clear gas appliance intake and exhaust vents after every storm. After a lake effect snow, check that drifts have not buried furnace vent pipes on an outside wall.

Why does my furnace smell musty?

A musty smell points to moisture. Lennox says it can simply mean the system has not run in a while, but if it persists there could be mold or mildew. Carrier names the ducts and the furnace mounted cooling coil; Trane adds the filter.

• The filter. Put in a fresh one.
• The drain pan under the AC coil, which catches its water. The EPA's duct guidance says cooling coils can be a major source of moisture in a system, and that substantial standing water in the pan needs immediate attention.
• Basement humidity. The EPA's mold guide advises keeping indoor humidity below 60 percent, ideally 30 to 50 percent.

If the smell stays after a new filter, or you can see mold, stop running the system. The EPA says running one you know or suspect is contaminated could spread mold through the building, and that mold comes back unless the moisture is fixed. If that leaves you without heat in a cold snap, call. Dehumidifiers and UV lamps at the coil are on our indoor air quality page.

How can I cut down the first run smell?

1. Start the season with a clean filter, as Trane recommends. ENERGY STAR's maintenance checklist says to inspect, clean or change it once a month.
2. Clear the area around the furnace. The U.S. Fire Administration's heating safety handout says to keep anything that can burn away from the furnace.
3. Check the registers. Carrier suggests lifting floor vents to look for dirt and foreign objects.
4. Have the furnace checked in the fall. ENERGY STAR recommends a fall heating check covering gas connections and pressure, burner combustion, the heat exchanger and electrical connections. The EPA recommends servicing a fuel burning furnace before each heating season to protect against carbon monoxide.
5. Test the CO alarms when the furnace is checked, and monthly after that, as CPSC advises.
6. Run the heat for the first time on a mild afternoon, not at bedtime on the first freezing night. Windows can stay open, and you are awake to notice whether the smell fades.

When to call Raber HVAC

• Gas, smoke, a CO alarm or CO symptoms: everyone outside, then 911 or your gas utility. Once the house is safe, call us to check the furnace before it runs again.
• A burning plastic, rubber or wiring smell, a dusty smell that keeps coming back, or a musty smell a new filter does not fix: turn the furnace off and call (216) 888-4822 for furnace repair. The office is open every day, 8:00 AM to 10:00 PM.
• No heat in freezing weather after shutting it off: call the 24/7 emergency line on the same number, which also covers active water leaks and sewage backups. While you wait, use an electric space heater only: the U.S. Fire Administration says to plug it straight into a wall outlet, keep it at least 3 feet from anything that burns and turn it off when you leave the room or go to bed. Never heat with a gas oven, grill, camp stove, patio heater or generator, indoors or in the garage: they make carbon monoxide, and between them the CDC and Enbridge rule out every one. See what counts as an emergency.
• Anything that can wait a day: book online, pick a day and an arrival window, and the office calls to confirm.

Sources

• Carrier, Burning Smell in House? Causes and Solutions for Furnace Odors
• Trane, Help! My Furnace Smells Like Burning
• Lennox, Does Your Heater Smell Like It's Burning?
• Enbridge Gas Ohio, Smell Natural Gas? What to Do Right Away
• Enbridge Gas Ohio, Energy Choice
• Enbridge Gas Ohio, Carbon Monoxide Safety
• CDC, Carbon Monoxide Poisoning Basics
• U.S. Consumer Product Safety Commission, CO Alarms
• U.S. Consumer Product Safety Commission, Carbon Monoxide Information Center
• U.S. EPA, Should You Have the Air Ducts in Your Home Cleaned?
• U.S. EPA, A Brief Guide to Mold, Moisture and Your Home
• ENERGY STAR, Maintenance Checklist
• U.S. Fire Administration, Heating Fire Safety handout
• Ready.gov, Home Fires