Ultravation News and Information Center

What is MERV?

If you have looked around the Ultravation website, or most other air filtration sites, you’ve probably come across the term “MERV”. And, you’ve probably figured out that the higher the number, the better the filter. But, do you really know what “MERV” means?
MERV, or Minimum Efficiency Reporting Value, is a way to measure the effectiveness of an air filter. ASHRAE (the American Society of Heating, Refrigeration and Air Conditioning Engineers) created this measurement method. The numbering system denotes how effective an air filter is at capturing various sizes of particulates. A lower number indicates that the filter will collect larger sized particulate, but the smaller particles will generally pass through it. A higher number indicates that the filter can collect more of the larger particulate, as well as, a majority of the smaller particles. For example:

This system is based on the percentage of the smallest particles an air filter can capture, so particulate larger than 10.0 microns, such as most pollen and dust particles, won’t appear on the scale. To put this amazingly tiny measurement into perspective, there are 25,400 microns per one inch of human hair, and there are 300 microns across its diameter!
As the MERV rating increases so does air flow resistance, or what is known as “pressure drop”. When you put a high MERV-rated filter in an HVAC system, you are placing more filtering media in the path of airflow, which can cause lower pressure on the downstream side of the filter. This means your HVAC isn’t moving the air though the ductwork as fast, which can make the system take longer to do its job. That being said, using a quality filter will help keep pressure drop minimized. For example, Ultravation’s ProgressiveMedia™ MERV 11 filters actually have a pressure drop rating of a MERV 8, which is not something many other companies can say.
So now that you know a little more about MERV, you can better decide what air filter is best for your HVAC system and your indoor air environment. Be sure to research what your HVAC unit can handle before purchasing an upgraded air filter. If you usually use a MERV 4 and then switch to a MERV 13, it could potentially be problematic for your HVAC system. Contacting an HVAC professional to discuss your options is always recommended.