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Air Filter MERV Ratings and Why You Should Care

MERV Chart | Gary Smith - Central MS Home Inspections and Energy Evaluations
Image by FilterFast.com

We spend more time indoors during the winter months. That’s why it makes sense to keep your heating and cooling system’s air filter changed. Here are a few details to consider.

Air filters are manufactured with a rating called the MERV or minimum efficiency reporting value.  That’s a number from 1 to 16 that’s relative to the filter’s efficiency. The rating was designed by ASHRAE in 1987.

The higher the “MERV Number”, the more efficient the air filter is at removing particles and contaminates from the air you breath.  The cheap ones you purchase as the grocery store (please don’t buy these cheap air filters) often have a MERV rating of below 4 or 5. At the higher end, a MERV 14 – 16 filter is typically the filter of choice for critical areas of a hospital (to prevent transfer of bacteria and infectious diseases). Read More About MERV Ratings.

Start out by matching your MERV rating to your heating system manufacturer’s recommendations. If the filter doesn’t allow enough air to be drawn through it there is a potential for damage to your heating and cooling blower motor.

Generally, the fan motor on a typical heating and cooling system is not strong enough to easily pull air through a filter rating above a MERV 6-8 (consultant your HVAC contractor – or call us – for help in determining a safe MERV rating/size). Also, the extra load on the heating system fan will use more energy than it should, driving up your energy bill.

On average I recommend you change your air filter every 60 days. A few factors that would/could alter that time frame are:

  • You live on a dusty road. Even if you can’t see the dust in the air, it’s present.
  • Your fan motor runs often. Longer run times will filter more particles.
  • You’re using a high MERV rated filter. The higher the filter the more often it should be changed.
Here’s an example of why keeping a clean filter can keep you warm in the winter. See the air loss through a dirty filter.

Get Air Filter Delivered to Your Door

Filtrete 9801-6PK Micro Allergen Reduction Filters, 1000 MPR, 16 x 25 x 1, 6-Pack

Home Inspector – Home Builder and Building Consultant/Coach

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