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.