What is a MERV rating? And why Bigger isn’t always Better.

As air moves through your home’s HVAC system, air filters trap and gather large and small particles such as dust, allergens, and microorganisms.  This filtration helps provide safer indoor air quality.  A filter’s MERV number indicates how it’s rated to remove these particles.  What is a MERV rating, exactly?

MERV stands for Minimum Efficiency Reporting Value and measures how effectively the air filter stops dust and other contaminates from passing through the filter and into the air stream.  Filters with higher MERV ratings stop small particles more effectively than filters with lower MERV ratings.

Generally speaking, air filters with a rating of MERV-16 or below are considered standard-grade filters for residential use.  MERV 17-20 filters are typically used in surgical operating rooms, clean rooms, and in other contexts that require absolute cleanliness.

When selecting the MERV rating for your home air filter, higher is not always better.  Utilizing an air filter with a MERV rating higher than what your furnace manufacturer recommends can actually impair it’s performance.  

The smaller pores in higher MERV rated filters create resistance to air flow, and if the filter is used in a furnace that is not designed to handle this added resistance, it can lower the system’s efficiency, decrease indoor air quality, and strain the unit’s fan, leading to unwanted repairs.

Studies show there is a connection between larger amounts of particles in outdoor air and poor health, so it’s natural to apply that connection to indoor air as well.  Filtering these particles from your indoor air could lead to better health.  This filtration could be effective against allergy and asthma symptoms and communicable illnesses.  Use the MERV rating chart below to understand which filters are best for what applications.

“The Complete Air Filter MERV Rating Chart – Grainger KnowHow.” 11 Feb. 2020, Grainger Editorial Staff

In conclusion, when thinking about the MERV rating on your home’s air filters, while a larger number may seem appealing, it can do damage to your home’s HVAC system.  Be sure to check the  furnace manufacturer’s recommendation before upgrading your home’s air filters.  If you have any questions, please call our experts for help and/or recommendations.

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