What's a MERV and why does it matter?

Minimum Efficiency Reporting Value (MERV) is a score that is given to indoor air filters by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). This rating helps quickly communicate the size of particles the air filter is designed to capture, giving homeowners an easy way to find the right filter for their homes. 

For residential filters, you'll notice the most common ratings ranging from 4-13. The larger the number, the better the filter is at catching smaller particles. 

So you're probably thinking you should just buy the filter with the highest rating, right? Not necessarily. There are a few things you need to know about filters with different MERV ratings.

  • Higher MERV rated filters have a larger pressure drop, which means that your airflow is slowed down as it passes through the filter. This can put extra strain on your furnace, so it is important to know your furnace's capacity. Check with your furnace provider or read your manual to find out your maximum capacity.
  • Filters with higher MERV ratings are more expensive, but they need to be changed less frequently. 
  • You should choose your filter based on your indoor air qualities goals and needs, not just the highest rating. 

This table will help you understand the different MERV ratings and what they protect against.

 MERV  Efficacy Contaminants

4 - 6

75-90% Pollen, Dust Mites, 

7 - 10

90-95% Mold Spores, Hair Spray, Auto Emissions


95-98% Milled Flour, Humidifier Dust, Pet Dander


>98% Proplet Nuceli (Sneeze), Tobacco Smoke, Bacteria