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Air Filters: Why A Higher MERV Rating Isn't Always The Best Choice

April 18, 2013 | Blog

Air filters can play an important role in your home, protecting both your HVAC system and your lungs. There are many different types of air filters available, which naturally raises the question of which filter you should use. 

One popular way to compare air filters is to look at their MERV ratings. People commonly assume that a higher MERV rating equates to a “better” air filter. However, that is not always the case.

What are MERV ratings?

MERV, or Minimum Efficiency Reporting Value, is a scale for measuring how effective air filters are at removing tiny particles from the air.

Filters are tested in laboratory conditions, and the lowest (“minimum”) score from those tests is used to determine the MERV rating. MERV is a 20-point scale; higher numbers indicate that a higher percentage of smaller particles is filtered from the air. However, residential air filters almost never rate above 16 on the MERV scale, and in many cases you may not actually want a filter with a very high MERV rating.

Why a higher MERV isn’t always better

There are several reasons why MERV ratings are not necessarily the best gauge to use when choosing air filters:

  • Restricted airflow. To filter out tinier particles, a high-MERV filter must be woven more tightly and have smaller openings for the air to pass through. Less airflow means that your HVAC equipment will have a harder time keeping your home comfortable, and will use more energy. Using pleated filters can help, but air filters with very high MERV ratings would likely require a different ductwork design or stronger fan motor to compensate for the airflow issues.
  • Lifetime performance. MERV measures the minimum efficiency, not the average efficiency. Sometimes, filters with mediocre MERV ratings can have a better lifetime performance than those with higher MERV ratings.
  • Electrostatic degradation. Electrostatic filters can earn high MERV ratings in the lab, but do not work nearly as well in our humid air.

No matter what grade of air filter you choose for your home’s HVAC system, make sure you inspect it once a month, and replace it when it gets dirty.  Any filter that you use should be sized large enough to handle the amount of air it needs to.

At CCAC, Inc., we can help you sort through the options and find the best air filter for your Coastal Bend home. Please contact us with any questions.

Our goal is to help educate our customers in Corpus Christi, Texas about energy and home comfort issues (specific to HVAC systems).  For more information about Air Filters and other HVAC topics, download our free Home Comfort Resource guide.

Image courtesy of Shutterstock

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