3 Reasons Your Furnace Smells When Operating

Your home's furnace is designed to warm your home, not make it smell. If your furnace is transmitting an odor when operating, this should be cause for concern. Here are just some of the reasons your furnace might be producing an unusual smell.

Burning Smell

A burning smell can occur for a number of different reasons. On one hand, it can be a minor issue. If you live in a home where the registers are on the floor, a small toy trapped inside or a spill can produce a burning type of smell. If you can remove the toy or clean up the spill, you can resolve the problem.

This smell can also be attributed to a more serious problem, like internal electrical damage, such as a cracked exchanger or a defect with the motor. If your furnace smells like it's burning and you can't clearly see a problem with a register, turn off the unit and call a professional right away.

Musty Smell

If you're operating a furnace that has a humidifier filter attachment, you could be dealing with a mold issue if you are smelling a musty odor. Humidifier attachments distribute moisture throughout your duct system to keep the air inside your home at a comfortable humidity level. However, the filter is also designed to trap contaminants.

When the filter gets clogged, instead of the moisture making its way into the ducts, it gets trapped in the filter and leads to mold growth. Once mold has developed on the filter, it will transmit the musty odor throughout your home. If you're dealing with this smell, it's time to change your humidifier filter.


If your furnace has a smoke-like smell when operating, this is often attributed to a problem with the chimney. Some furnaces have a small chimney or flue on the roof of the home designed to release the fumes from an oil or gas furnace. When this structure is blocked, instead of the air escaping your home, it gets forced back through the furnace.

When air is forced into the furnace from the exit point, this can produce a smoke smell. In many instances an animal nest is the reason for the blockage. Make sure you have this matter resolved promptly, as a block can also force dangerous gases back inside your home.

When diagnosing a smell, always rely on the expertise of a professional. If your unit is producing a smell, don't hesitate to contact an HVAC professional like SDA Armstrong Mechanical Services Ltd for assistance.