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What Is Your Furnace Air Filter Made Of?

The indoor air quality (IAQ) in your Fairfax, Virginia, home depends partially on the kind of filters in your furnace. Furnace air filters protect the furnace mechanisms from getting dirty and also remove particles from the air you breathe. Filters are made of different materials including fiberglass, polyester, and cotton. The type of material affects how effectively the furnace filters the air.

Furnace Filter Ratings

Air filters for your HVAC system are rated on the Minimum Efficiency Reporting Values (MERV) scale with a number from one to 20. The higher the number, the better the filter is at removing particles from your indoor air. Your furnace will be rated for a certain MERV — don’t use a filter higher than that rating, or you risk forcing your blower to work harder.


These are lowest on the MERV scale, with ratings generally from two to four. They are the filters you’ll find in most furnaces, and are made of spun fiberglass about an inch thick. They protect your furnace from dust, but don’t do much to improve IAQ. They are very inexpensive, so if you don’t have serious respiratory problems, you may not need anything more than disposable fiberglass filters.

Pleated Fabric

Disposable pleated filters are made of polyester or cotton paper sheets and are better at trapping particulates. They are generally rated from six to 13 on the MERV scale. Cotton filters have higher ratings and their fibers can self-charge to remove smaller particles from the air. They usually have a MERV rating of 10 or higher and are slightly more expensive than the typical pleated variety.

Washable Fabric

Furnace filters are generally disposable, but you can choose those that are washable. You can buy washable electrostatic filters which are rated at eight on the MERV scale.

While washable filters can last from six to eight years and might be more convenient in some ways, they do not have a good reputation among homeowners. They have been known to develop bacteria and fungus, and they don’t come with the high MERV ratings that many homeowners want.

HEPA Filters

High-Efficiency Particulate Air (HEPA) filters generally have MERV ratings of 17 through 20. They are the most effective for cleaning the air in your home but aren’t practical for most HVAC systems since the filters are so thick. Typical furnaces will have to work very hard to push air through them. If your equipment is not rated for HEPA filters, it’s a bad idea to use them. Unless you’re an asthma sufferer or have severe allergies, you don’t need a HEPA filter.

If you have questions about what kind of filter your furnace can handle, or need assistance improving your IAQ, call Brennan’s Heating and Air Conditioning today at 703-783-0145.

Image provided by Shutterstock

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