Why Your Furnace Has a Strange Smell

As the weather turns cold and you transition from cooling to heating your home, you might be worried about strange furnace smells floating in the air. Learn what the most common furnace smells mean and how proactive you should be about them.

The Furnace Smells Musty

Musty furnace smells usually imply mold growth hiding in the HVAC system. To avoid subjecting your family to allergy-inducing mold, tackle this problem right away.

A clogged air filter can encourage mold, so eliminating the smell could be as easy as swapping out filter. If that doesn’t work, the AC evaporator coil placed near the furnace might be to blame. This component collects condensation, which can induce mold growth. You’ll need a professional’s help to check and clean the evaporator coil. When the problem still won't go away, take a look at requesting air duct cleaning. This service cleans away hidden mold, regardless of where it's hiding in your ductwork.

The Furnace Smells Like Spoiled Eggs

This is one of the most worrisome furnace smells since it probably suggests a gas leak. The utility company includes a special substance called mercaptan to the natural gas supply to make leaks more easily detected.

If you recognize a rotten egg smell around your furnace or originating from your air ducts, shut down the heater right away. If you remember where the main gas supply valve is located, shut that off as well. Then, leave the house and call 911, as well as your gas company. Don’t enter the house until a professional confirms it’s safe.

The Furnace Has a Sour Stench

If you notice a sour smell that stings your nose while standing near the furnace, this might mean the heat exchanger has cracked. This essential component safely contains combustion fumes, including carbon monoxide, so a cracked heat exchanger might spew unsafe levels of CO gas into your home.

Carbon monoxide poisoning can be lethal, so switch off your furnace right away if you notice a sour odor. Then, contact an HVAC professional for an inspection. Consider replacing your furnace if a cracked heat exchanger is the culprit. For your family's safety going forward, ensure you have reliable CO detectors on each floor of your home.

The Furnace Smells Dusty

When you turn on the furnace for the first time after a while, you probably expect a dusty odor to fill the house for a little while. This is the smell of six months’ worth of dust burning up as the furnace wakes from its summer slumber. As long as the smell goes away within one day, you don't have anything to worry about.

The Furnace Has a Smoky Smell

Natural gas, oil and propane furnaces are combustion appliances, so they vent fumes safely out of your home. A smoky smell can mean the flue is backed up, and now fumes are settling back into your home. The odor can reach through the entire house, risking your family’s health if you ignore it. So shut down the furnace and call a professional right away to arrange for repair.

The Furnace Smells Like Burning Plastic

Overheating and burned electrical components are the most plausible reason for a burning plastic smell to make an appearance. A malfunctioning fan motor is another common cause. If you don’t tackle the problem, an electrical fire could start, or your furnace could end up with irreparable damage. Turn off the heating system as soon as possible and call an HVAC technician for help troubleshooting and repairing this weird furnace smell.

The Furnace Has an Oily Smell

If you use an oil furnace, you might detect this smell if the oil filter becomes blocked up. Try replacing it to find out if that addresses the problem. If the smell lingers for more than one day after completing this step, it might indicate an oil leak. You’ll need help from an HVAC professional to fix this problem.

The Furnace Reeks of Sewer Odors

Sewer gas smells pretty similar to spoiled eggs, so first determine the potential for a natural gas leak. If that’s not the source, your sewer lines could have an issue, like a dry trap or sewer leak. Flush water down the drains, including the basement floor drain, to replenish dried-up sewer traps. If the smell lingers, you’ll need to contact a sewer line repair company.

Contact Komfort Air Service Experts for Furnace Repair

When in doubt, call an HVAC technician to examine and repair your furnace. At Komfort Air Service Experts, we deliver comprehensive diagnostic services to determine the problem before the work begins. Then, we suggest the most viable, cost-effective repairs, alongside an up-front estimate for all options. Our ACE-certified technicians can manage just about any heating repair, and we back our work with a 100% satisfaction guarantee for one year. For details about why your furnace smells bad or to request furnace repair near you, please contact your local Komfort Air Service Experts office today.