Why Your Furnace Smells Like It’s Burning When You First Turn It On

Why Your Furnace Smells Like It’s Burning When You First Turn It On

It’s time to switch off summer air conditioning and turn on the heat. When you do, your home fills with a distinct odor. Sometimes, that odor is harmless and is simply the smell of dander, dust, and pollen that’s settled on baseboards or registers since you last ran your heat.

Sometimes, however, the smell indicates a dangerous problem with your heating system. Knowing what odors are normal and when you should be sounding the alarm and calling an emergency HVAC repair team is essential for your safety.

The Most Common HVAC Odors and What They Can Mean

Here’s a breakdown of the most common odors and what might be wrong. In some cases, it might not be a big deal. In other situations, you need to get to safety and then call emergency services or HVAC technicians.

Burning Dust

The smell of burning dust is incredibly common. After months of sitting unused, dust often builds up on floor registers or baseboard fins. As the heating system warms up, the dust, dander, and pollen start to burn, creating the burning-dust odor that can fill your house for a couple of hours.

If your air filter is clogged, you might also notice a dusty odor. Replace your filter as soon as possible. 

Burning Oil 

If you smell burning oil when your heater starts up, it can be a sign of a dirty burner. Oil isn’t being burned completely. The same can happen with low fuel pressure, a dirty filter, or a clog in the fuel line.

Another problem that can make your home smell like burning oil is a clogged vent pipe. A mouse could have gotten into the exhaust pipe from outside and built a nest, or a bird could have blocked the end of your chimney.

Electrical Smells

There’s a distinct smell when something electrical is burning. It can smell like melting plastic, strong chemicals, or metal. If the plastic coating on the wire is melting, you will smell melting plastic. If older components have flame retardants, it can smell like rotting fish or ammonia.

Gas, Sulfur, or Rotten Eggs

If you have a gas system, a rotten-egg, sulfur, or gas smell can indicate a potential gas leak. Go outside and call your gas company. This is an emergency and not something to put off. Call now.

Once the leak is confirmed, you need to have it fixed. That may require an emergency HVAC technician to repair any parts that are worn on your furnace.

Hot Metal

The smell of hot metal can be tied to many things. It can be worn blower motor bearings or internal components rubbing together and causing friction. It can also be tied to an electrical issue.

If you just had a new furnace installed, you may smell an odor similar to burning oil or hot metal while the special coatings and lubricants burn off. Usually, these odors dissipate after an hour or two. 

Melting Plastic

Melting plastic odors may be caused by the coating on wires melting because of an electrical issue. Your blower might be having problems. 

Moldy and Musty

If you smell musty or moldy odors after turning on your furnace, you likely have an issue with mold in your ducts. In high humidity, mold thrives, and it doesn’t just disappear as winter arrives.

Sewage

If your furnace is connected to a central AC system, sludge that builds up during the summer may develop a sewer-like smell when your heating system heats up.  

High-efficiency furnaces with condensate lines can smell like sewage if a floor drain or P-trap dries out, allowing sewer and septic gases to enter your home and get into your ducts. It’s also worth looking at your ducts to make sure no mice or rodents entered through a hole or crack and died.

What Do You Do Next?

Aside from dust odor that just needs to burn off, we don’t recommend a wait-and-watch approach for any odor after turning on your heat for the season. You need to respond appropriately to different smells.

Burning Plastic/Electricals

If you suspect an electrical issue and see sparks and flames, don’t delay. Turn off the breaker, if you can, get your family members and pets, and get out. Once you’ve safely evacuated, call 911 and let the experts determine the issue and ensure your home is safe to enter.

Check the Filter

Some smells are as simple as having a dirty filter. Remove it and hold it up to the light. Can you see light through it? If not, it’s dirty and needs to be replaced. Make sure you replace it with the same MERV rating. If you pick a rating that’s too high, you restrict airflow to your system.

Gas/Oil 

If you smell gas or oil, or your carbon monoxide or smoke detectors go off, get outside and call emergency HVAC or emergency services.

Mold or Sewage

For other odors like mold or sewage, have your system inspected for common issues like dirty ducts, blocked drains, or sludge in a condensate pan. Have those cleaned by a professional. 

If you suspect a bird, chipmunk, mouse, or squirrel got into your chimney or vent pipe, check the outside of the pipe to see whether a screen or cap is installed to keep them out. If you don’t see one, ask your HVAC company whether there’s a reason one wasn’t installed.

Noises

Pay attention to any unusual noises throughout the season. If there are parts rubbing together or bearings or motors are starting to wear out, you’ll hear it. The sooner you repair those issues, the better. If you wait too long, you could end up with damaged HVAC equipment and a pricey repair bill.

Schedule Yearly Maintenance and Avoid Surprises

When you have your furnace cleaned and inspected each year, you avoid some surprises. When an HVAC technician cleans your furnace, they inspect essential components. If anything looks like it’s wearing out, you can replace it before it fails and damages other components. 

Air Blue Heating and Cooling offers comprehensive furnace check-ups that clean, inspect, and test the following components, as well as many others.

• Blower motors and wheels
• Burners
• Circuit boards
• Drains and traps
• Ducts and plenums
• Electricals
• Filters
• Flame sensors
• Flue pipes
• Gas valves
• Inducer motors
• Thermostats

Our technician also checks for carbon monoxide leaks. If anything is amiss with your furnace, we can repair it. Our repairs are backed by a two-year warranty. Schedule a furnace check-up today.