Learn 4 Types of Whole House Air Filters – How Do They Work?

1. Flat Filters

If you have a forced-air furnace, you already have a basic air-filtration system: that matted-fiberglass filter that should be replaced once a month. “You can’t change it often enough,” says plumbing and heating expert Richard Trethewey of This Old House.


It stops working and overworks the furnace when it becomes clogged with dust. In truth, those filters are intended to protect your furnace from massive dust particles, and while they may keep surfaces in your home cleaner, they will not block the small particles most irritating to lung tissue. Pleated filters, which pack more material into the same area, are slightly more expensive but perform somewhat better.

By far, the most effective pleated filters are electrostatically charged to attract allergens such as pollen and pet hair.

They are about $15 each and should be replaced every two to three months.

2. Extended Media Filters

Consider an extended media filter a stack of furnace filters about 8 inches thick. These boxy units include an accordion-style pile of filtration media, making them more effective than standard fiberglass filters. Because the huge filter holder must be plumbed into the ducting, they require professional installation. The price, including installation, runs from $400 to $600; the $40-to-$60 filters must be replaced every year.


3. Electronic Filters

These high-tech machines, also known as electrostatic precipitators, are built into the ducting. A high-voltage current charges particles as they move through the air. At the other end of the unit, oppositely charged collection plates act like magnets, attracting particles.

Electronic filters perform exceptionally well on smoke particles that are too tiny to be caught by media filters. According to one independent test, such filters performed nearly 30 times better than standard fiberglass filters.(Because performance is affected by a home’s blower and ductwork, there is no industry benchmark for gauging the effectiveness of whole house systems.)