Air Filters

Air filters can combat indoor pollution by capturing allergy causing particles like pollen, mold, and pet dander. A dirty filter can waste energy by slowing down air flow making your heating or cooling system work harder to maintain desired temperature

There are many different types of filters. Some air filters that are highly efficient at removing certain types and sizes of particles may be inefficient at removing others. Particles smaller than ten microns in size (one sixth the diameter of human hair), that are not visible to the naked eye are of the greatest health concern.

Full-house (central) filters can be rated in a number of ways. Current standards use the Minimum Efficiency Reporting Value (MERV). MERV is expressed as a number between 1 and 20.

Central forced air systems in homes usually have a rectangular, one-inch thick fiberglass filter that slides underneath the furnace fan or into a wall or ceiling register where the air returns to the furnace. These filters are most effective at removing particles 10 microns in size or larger, and typically remove less than 10% of the very small particles that reach the filter. They are disposable.

Very low-efficiency type filters are often rated by weight “arrestance”. Weight arrestance is NOT efficiency. It is the percent of weight, in grams of dust, which the filter can hold before it loads up completely. It is a measure of the filter’s ability to handle coarse particulates and prevent physical damage to the air handling system. MERV ratings for such filters are usually between 1 and 4.

Medium-efficiency filters are typically pleated, woven material and are rated at 20-50% efficiency for removing particles of 0.3 to 10 microns. Both disposable and washable models are available. MERV ratings for such filters are usually between 5 and 8.

High-efficiency filters are rated at 0- 95% efficiency. Both disposable and washable models are available. They are sometimes mistakenly called “HEPA” filters, however, true HEPA (High Efficiency Particle Arrestance) filters are 99.97% efficient. These are available from an HVAC professional.

MERV ratings for such filters are 9 and over; the top-performing models tested by Consumer Reports have had a MERV of 11 to 13. MERV ratings do not apply to electronic air filters.
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