Common causes of a burning smell and when to get expert help

After months of disuse, a burning smell from your furnace or air handler can be common, but that doesn’t mean there isn’t cause for concern. There can be several reasons for the odor, and some come with simple fixes. Troubleshooting on your own to determine the source is a good first step before seeking professional help; and can save you on repair costs.

Common Reasons for a Burning Smell in Your Heater

Accumulated Dust and Debris
The most common cause for the burning smell is accumulated dust and debris in the heating system. When you turn off your furnace during the warmer months, it will collect dust when it’s not in use. The dust builds up on the inside of the unit and ignites when you initially turn it on, resulting in a burning smell. Fortunately, accumulated dust shouldn’t be cause for concern as the smell should not last for long. Let your unit run for an hour or two and the smell should subside or disappear.

Dirty or Clogged Filters or Vents
Your heating system could be overworking due to dirty or clogged air filters. Old filters can also lead to mold and mildew to grow inside ductwork, causing a musty odor. Turn off the unit and check your air filters and vents to ensure they are clean. Frequently changing your air filters every three months will help to maximize performance.

Foreign Objects in the Heating System
If you’re smelling a plastic burning smell, it's possible a foreign object(s) could be lodged in your unit, vents or ductwork. Small items can often end up in the system during the warmer months and when initially turned back on, it can create that burning smell. Burning plastic contains harmful fumes that could be harmful to your health. Switch off the unit and inspect your vents. If there are visible objects, safely remove them and wait to see if the smell subsides.

Damaged Electrical Wiring
Damage can occur to wiring over time or have issues due to incorrect installation. If the odor is metallic, this could be a sign of a serious electrical problem. An overheated blower motor or wiring harness are major causes of faulty electrical wiring. Many systems have a safety feature where it will shut down when overheating, but if that is damaged, there will be a burning smell along with a risk of an electrical fire. Immediately turn off your unit and inspect it for damage. If you suspect an electrical issue is the problem, contact an HVAC professional immediately.

Gas Leaks
Smelling gas in your home is never a good sign and could mean your furnace is leaking gas. Natural gas can also have an odor that smells like rotten eggs. Before attempting any repairs yourself, contact your utility company immediately to help diagnose any problems with your gas line. Because gas is flammable, it is best to evacuate your home until the problem is fixed buy a professional.

Bacteria and Mold Buildup
If you smell a musty odor, it could simply mean your system hasn’t been used in a while. If the smell persists, there could be mold or mildew in the system or the ductwork. Bacteria can build up in areas where it is difficult to clean. Cleaning your air ducts is the best way to remove the smell.

Chemical Odors from New Furnace
When a new furnace is initially heated, its protective finish starts to burn, which can cause a mild, chemical-like smell. Let your unit run for a few hours in a well-ventilated home and the odor should disappear.

Preventing the Burning Smell in Your Heater

While not all heater odors are avoidable, some steps can be taken to reduce the potential of some of the common culprits.

Replacing Air Filters Regularly
Air filters are designed to collect dust from the air. The more dust they accumulate makes them less effective over time and can contribute to odors. Replacing them every three months will ensure maximize performance of the unit.

Cleaning Exterior Surface
Before starting your furnace for the season, make sure to thoroughly clean the area around the unit. Dust and debris can accumulate, and foreign objects can land by it if it hasn’t been used for an extended period.

Regular Maintenance
Scheduling a professional tune-up at least once a year in the fall with your HVAC professional will help your unit run smoothly and prevent unwanted smells. A professional can calibrate the thermostat, test the wiring to ensure electrical connections are secure and functioning correctly and replace worn parts. Regular maintenance can help your unit use less energy and run more efficiently so it can last longer. To learn more about furnace tune-ups and why they are important.

When to Seek Professional Help

In most cases, a burning smell isn’t cause for concern, especially when the unit is first started after not being in use. But, if the smell persists or gets worse despite the troubleshooting attempts mentioned above, there could be severe electrical problems, damage to the unit or components that are worn out or malfunctioning. In these scenarios, it is best to contact a qualified professional for help instead of attempting to do it yourself and risk worsening the issue. Find a Lennox Dealer in your area to schedule an inspection to determine the cause of the burning smell in your heater.