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Furnace Filters: Clean the Air

Posted by Ron Wolford -

You may be surprised to learn that the air inside your home may be more polluted than the air outside, even if you live in a large industrial city. Considering the fact that most people spend 90 percent of their time indoors, indoor air quality is a serious health concern.

"Furnace filters are designed to keep the furnace system clean," says Lois Smith, consumer and family economics educator with University of Illinois Extension. "The air filtering system can also contribute to good health for family members by cleaning the air circulating throughout the house."

There are several types of furnace filters available. Selecting the one that suits your needs can sometimes be confusing.

Panel filters are the typical furnace filters used in homes. The primary function is to protect the furnace fan and keep dust on the coils to a minimum. These filters catch large particles from the air.

Washable filters can be washed and reused. These filters do not catch small particles.

Pleated filters have a larger surface to collect particles, so they are typically more efficient than the panel filters.

High efficiency pleated filters are designed to catch small particles such as dust, pet dander, smoke and mold.

High Efficiency Particulate Air (HEPA) filters remove sub-micron particles. However, they are not designed to fit most standard furnaces.

Electronic air cleaners use an electrical field to trap charged particles and are considered the most effective as well as being more expensive.

"An important point to remember regardless of which kind of furnace filter you select is that filters will become filled with particles, and efficiency will change over time," says Smith. "These filters need to be replaced on a regular basis following manufacturers' instructions to insure proper airflow."

Electronic systems are considered the most efficient when first installed, but they lose their efficiency as they get dirty. Regular maintenance and cleaning are required to keep these systems operating at peak efficiency.

Smith says to replace your filter at the stated intervals, usually about every three months. Replace more often if you are introducing high levels of pollutants into your home, such as when remodeling, when using candles, if someone smokes in your house or if you have a pet in the home. Consider more frequent replacement if you have a family member with asthma, allergies or other lung problems.

Furnace Filters, a University of Illinois Extension fact sheet, provides information on different types of filters, features to look for, and maintenance requirements. Contact your local U of I Extension office for a copy, or view the Solution Series web page at

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