Have you ever heard of the Minimum Efficiency Report Value (MERV) rating for air filters? It's a rating system designed by ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) to measure the effectiveness of air filters. In short, a MERV rating lets you know what particle size of air an air filter will trap. A higher rating means that the filter can trap smaller air particles. Not all filters are created equal, so the higher the number, the better the filter.
Although your HVAC system may not handle a larger number, it's important to understand what a MERV rating is and how it works. MERV stands for “Minimum Value of Efficiency Reports” and it measures how effectively an air filter prevents dust and other contaminants from passing through the filter into the air stream. The scale ranges from 1 to 20, with 1 to 6 being the lowest range of MERV ratings. That doesn't necessarily mean you should cancel a filter with a rating in this range, however.
For example, if you have someone in your household who suffers from allergies, you may want a higher MERV rating. Commercial grade air purification manufacturers, such as ISO-Aire, who offer a HEPA air purification system, are often asked about MERV filters. Filters that are MERV 16 to 20 are generally only found in hospitals, cleanrooms, and nuclear power plants. Unlike other scales, which emphasized the need to increase the number of particles passing through an air filter, MERV was designed to offer a balance between particle filtering and energy efficiency.
For public access buildings, air filters with a value lower than MERV 7 should not be considered. You might think that an air filter with higher MERV ratings would be more beneficial, but in some cases, it's not. Basically, the higher the MERV rating, the greater the air filtration capabilities of a particular filter. These scales have different ranges than the MERV rating, but they are usually measured based on similar factors. By increasing the size range of air particles to 3-10 microns, a MERV 13 filter will capture 90% or more of them at their worst.
