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Understanding MERV and ASHRAE's Recommended Filter Value

The Minimum Efficiency Reporting Value, commonly known as MERV, is a standard developed by ASHRAE that measures the overall effectiveness of air filters used in HVAC systems.

MERV values range from 1-16, with MERV 16 representing the highest value in filters that are not HEPA or ULPA. ASHRAE recommends using filters with a minimum of MERV 13 in all applications. If the existing HVAC system can’t accommodate MERV 13, ASHRAE recommends using the highest-MERV filters possible.


The main advantage of using high-MERV filters is, of course, cleaner, healthier air. And in 100% outside air systems, using higher-efficiency pre-filters can extend the life of HEPA filters downstream. The reality is, though, that many HVAC systems use filters with a value much lower than the recommended MERV 13.


Can I upgrade to a higher MERV in my existing HVAC system?


It is often possible to upgrade filter efficiency in existing systems, however, it’s rarely as simple as dropping in a MERV 11 where a MERV 8 used to be. Those considering filter upgrades should have an HVAC specialist like MSC evaluate their system to determine the highest MERV it can accommodate. Otherwise, too-efficient filters can seriously restrict airflow, degrade system performance, and significantly increase energy use. A professional can also determine whether the system can be altered to accept higher-MERV filters such as by modifying filter racks, increasing fan speeds, or other methods.


What else should I know about MERV?


Higher MERV means cleaner air, but it should be understood that these filters load faster and must be changed more frequently. During the spring pollen season, even low-MERV filters can become clogged within a matter of weeks, so high-MERV users must be extra-diligent with filter changes during this period. HVAC systems with high-MERV filters usually consume more energy than their counterparts, but it's unlikely that utility bills will increase substantially when filter upgrades are done properly. These added costs may be well worth the improvement in IAQ, and in pre-filtered systems they may be far outweighed by the savings achieved by having to replace expensive HEPA or ULPA filters less often.


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