The MERV System (Minimum Efficiency Reporting Value) was instituted to provide minimum efficiency values. When you first install your new filter, its efficiency is at its lowest point. That's because it hasn't built up enough dust and particles on the filter to help trap more dust and particles.

The MERV Rating will give you a worst-case scenario for the lowest amount of efficiency you can expect from your filter. This MERV System also measures the size of the particles a filter can trap. The scale that the MERV System uses can range from a MERV 1 to a MERV 16 (95%+ ASHRAE filter). The MERV System is an excellent tool when you know which contaminants you want to have filtered.

The MERV System tells you what size particles each type of filter can trap. These sizes are referred to as microns. To help put this system into perspective, a hair from your head is about 60-75 microns in diameter. Particles under 35 microns are not visible to the naked eye. You can't see most of the contaminants in the air. Pollen particles can range from 10 to 100 microns in size; dust from 0.5 to 5 microns; human dander, 10 microns or higher; etc. The majority of harmful particles are less than 5 microns in size.