MERVThe generally accepted North American method of determining filter efficiency is through testing of filters to the ASHRAE 52.2 standard.

The test returns a MERV rating (Minimum Efficiency Reporting Value) for the tested filter.

Filter efficiency is tested through 6 measured dust loads on particulate in the size range of .3 to 10 microns. The higher the MERV rating, the more effective the filter is at trapping sub-micron particulate.

*It should be noted that the ASHRAE 52.2 test procedure returns the MINIMUM efficiency value for the tested filter. In actual use, once the filters have been coated with particulate, the filter efficiency would be much higher than that reported through the test.

MERV Ratings for commonly used filter medias are as follows:

  • 100% Cellulose Media MERV 10: 50% – 65% efficiency on particulate in the 1-3 micron range.
  • 80/20 Cellulose/Polyester MERV 11: 65% – 80% efficiency on particulate in the 1-3 micron range.
  • Spunbonded Polyester – MERV 12: Greater than 80% efficiency on particulate in the 1-3 micron range.
  • 80/20 Cellulose/Polyester with Nanofiber Membrane – MERV 15: Greater than 90% efficiency on particulate in the 1-3 micron range and 85% – 95% efficiency in the .3 – 1 micron range.
  • Spunbonded Polyester with PTFE Membrane – MERV 16: Greater than 95% efficiency on particulate in the 1-3 micron range and greater than 95% in the .3 – 1 micron range.
  • HEPA Medias – MERV 17: 99.97% efficiency on .3 micron particulate.
  • ULPA Medias – MERV 19: 99.99999% efficiency on .3 micron particulate.