What is a Merv Rating? Minimum Efficiency Reporting Value (MERV) is a standard that rates the overall effectiveness of air filters. MERV values vary from 1 to 16. The higher the MERV rating the better the filter will be in trapping airborne particles. This is why all our Santa Fe Whole House Ventilating Dehumidifiers feature MERV 13 air filters. The powerful dual exhaust improves air circulation throughout the entire space, allowing the maximum amount of air to be treated in the shortest time. Dual exhaust dehumidifiers are recommended for all crawl space and basement applications.