Indoor air quality is effected by the quality and condition of your air filter. Air filters come in several different types, and each type has varying degrees of efficiency.
Filters have a minimum efficiency reporting value, or MERV rating, which measures their efficiency on a scale from 1 to 20. MERV ratings give you an easy way to compare filters, but you still need to know what the various MERV ratings mean if you want to get air filters that suit your needs.
The minimum MERV rating for devices such as window air conditioners is 4. A rating of 4 means the filter can catch particles less than 10 microns in size, which includes things like pollen and dust mites. These filters provide minimum filtration, and are more for protecting the HVAC equipment itself rather than cleaning your home’s air. Air filters that are rated in the 6-12 range are medium-efficiency filters. MERV ratings from 6-8 can catch particles 3-10 microns in size, which include mold spores and pet dander. In the 9-12 range, filters can catch some bacteria. Filters in the 9-12 range are considered superior for residential applications.