Photos of Key Items for Shoppers

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Photos of Key Items in Retail Air Filter Department

Why are filters important?

A furnace filter removes particulate from the air that can impact your lungs and reduce the effectiveness of your furnace.

While MERV ratings are important, the rating means little if the filters are not changed regularly and do not fit snugly into the slot on the furnace. Old filters reduce air flow. Poor fitting filters allow air to bypass the filter - defeating the purpose of the filter.

In 1999, ASHRAE - the American Society of Heating, Refrigerating and Air-Conditioning Engineers - adopted the voluntary industry standard #52.2. ANSI/ASHRAE 52.2 created the MERV system. MERV is short for the Minimum Efficiency Rating Value. The MERV system provides a standardized approach to comparing the effectiveness of filters on three ranges of particles. It is not a measure of the energy efficiency of the filter.

The MERV system rates filers on a 1 to 16 scale with 16 being the best filter at removing particulate. The U.S. Environmental Protection Agency (EPA) recommends a MERV 8 to 13 rating for schools. The American Lung Association's Health House and the National Center for Healthy Housing recommend a filter with a MERV rating of 10 or more.

Helpful resources:

Below is a photo of a typical filter with the MERV rating in the highlighted photo.

3M is a major producer of filters. The following photo is an 3M filter that uses the MERV rating. The highlighted filter describes the MERV system as well as 3M's Microparticle Performance Rating. In January 2006, 3M removed references to the MERV system.

The new 3M filters shown below do not review to the MERV rating system. Instead its only uses 3M's performance rating system. To find out the comparable MERV rating, go to www.3m.com/us/home_leisure/filtrete/541_comparison.html. 3M's decision to remove MERV ratings makes it very difficult for consumers to compare filters.

WIthout regard to the published MERV rating, there are some filters that will do little to protect the effectiveness of the furnace and the health of the residents. The highlighted photo, the filter claims that it protects expensive equipment and helps remove allergens. It may do both at some level but not well enough based on EPA, NCHH and ALA recommendations. It does not have a MERV rating on it but is probably a MERV 4 or lower.

Another rating for a filter is called HEPA. HEPA stands for High Efficiency Particulate Air. A HEPA filter is a disposable, dry-type filter with a particle removal efficiency of no less than 99.97 percent for 0.3 micrometer particles. In contrast, a MERV 16 filter removed 95% or more of the 0.3 micrometer particles. HEPA filters are not recommended a furnace filters. They restrict the air flow too much. But they are excellent for vacuums and respirators. The photo below shows a retail HEPA filter.

10320 Little Patuxent Parkway, Suite 500 • Columbia, MD 21044
Phone: 410.992.0712 • Fax: 443.539.4150