Why is My Furnace Filter Dirty

Learn about pollutants and other factors that clog your filter

If your home is heated by a furnace, air circulates from room to room through ductwork. On its way to the furnace to be heated, air passes through a filter. This filter removes large particles that could settle on and damage the furnace. More efficient filters trap smaller particles to clean the indoor air. As you can imagine, furnace filters get congested the longer they are used. Learn why your furnace filter gets dirty and when it’s time to replace it.

• Pollutants that Clog Air Filters

• Dust, dirt and fibers - Dead skin cells, dirt tracked in from outside, and fibers from upholstered furniture, carpet and bedding all contribute to household dust. As these pollutants are whipped up, they enter the ductwork and clog up the furnace filter.

• Smoking indoors - Cigarette smoke wafts through the air when you smoke indoors, making its way to the filter and clogging it up faster than if you choose to smoke outside.

• Pet dander - Dogs and cats shed, which gets hair everywhere. Much of this hair is swept up into the ductwork, where the furnace filter catches it so it can’t re-circulate back into your home.

• Pollen - Even though flowers grow outside, it’s possible for pollen to hitch a ride on clothing, shoes, hair and skin. Furnace filters for allergy season are most effective at trapping pollen particles for cleaner indoor air.

• Mold spores - Efficient furnace filters for the home trap mold spores as they travel through the ductwork. If excess humidity dampens the filter, mold could start to grow here if you don’t change the filter frequently enough.

• Other Factors that Clog Up Your Filter Faster

• Cold weather - When the temperature drops, your furnace works harder to keep your home warm. This sends more air flowing through the filter and increases the amount of particles that become trapped there, dirtying your filter faster than normal.

• Thermostat set to on - This setting means the furnace blower runs all the time. Auto is a better setting for energy efficiency and helps your filter last longer as well.

• A home full of contaminants - More pets, people and dust in your home cause more contaminants to fly through the air. If you have multiple pets and people living at home, you should expect your furnace filter to become dirty faster.

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