MERV ratings are an industry-standard system for describing an air filter’s ability to remove small particles from the air.
Developed by the Engineering Association for the Heating and Cooling Industry (ASHRAE), the MERV ratings are an objective number, but they can be misleading. Air filters with high ratings often have issues with airflow, and a filter’s rating does not guarantee its reliability. Although the ratings are helpful, they don’t always indicate which filter is best.
High MERV ratings and restricted airflow
Air filters with high MERV ratings are prone to airflow problems because their openings are extremely small. As the filters’ pores become clogged, less and less air can flow freely through the filter. Even if a highly-rated filter is able to trap the tiniest particles, it’s useless unless air is able to move through it. Purchasing a filter with a lower rating lets air circulate more efficiently, so more of the air in one’s home is filtered.
MERV ratings over time
A filter’s rating comes from a laboratory test of six trials, which is not indicative of the average home environment. When the heater or air conditioning is running, air is constantly circulating through the filter. Over time, as the filter’s effectiveness diminishes, the MERV rating becomes less accurate. A filter that’s rated highly will not filter at the same rate after it is used for a month or even just a few weeks.
Selecting a filter for your home
In many cases, air filters with lower MERV ratings are better for a home’s air filtration than ones with an extremely high rating. Air filters with lower ratings tend to be less expensive and perform more consistently over time.
For more information about air filters and which one is right for your home, contact the experts at T.F. O’Brien Cooling & Heating. We’ve proudly served Long Island homeowners since 1934.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Resource guide.
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