AC Maintenance: Best Air Filter for Your HVAC System

AC Maintenance: Best Air Filter for Your HVAC System

AC Maintenance: HEPA Filters vs Merv Filters

We all acknowledge the importance of air filters since they successfully remove dust, pollen, dander, and mold spores. They clean indoor air but also keep dust from interfering with the function of HVAC systems. Filters are not composed of solid sheets, but are fibrous, with gaps to allow airflow. The size of the gaps determines the size of particles that are captured and thus, their efficiency.

Since filters collect airborne particles with each cycle, the filter eventually clogs and needs to be replaced. The Environmental Protection Agency and all manufacturers of HVAC equipment recommend changing air filters AT LEAST every three months. Fortunately, air filters are commonly available in a variety of home improvement and hardware stores. However, due to the size of the openings in the fiber, not all filters are manufactured equally—neither do they claim to be equal. Packaging for filters from various sources often touts various ratings with different acronyms and numbers; some explanations may be in order.

FPR Rating

Home Depot developed the Filter Performance Rating for their own brand of air filters; ratings are identified as Good, Better, Best, and Premium. The FPR rating for Good range between 4-5, Better have a range of 6-7, Best has a range of 8-9, and Premium filters have a rating of 10. With each upgrade, more particles are removed. While not exact, the ratings describe the size of the particles each rating collects and helps consumers understand their products.

MPR Rating

3M has also developed a rating for its Filtrete brand of filters. Filtrete filters are manufactured and marketed to remove specific airborne particulates. Some filters target dust and allergens, others target odors, and others seek to trap bacteria and viruses. MPR ratings use four digits—the higher the number, the smaller the opening. Consumer packaging denotes the percentage of the targeted particulate that will be removed.

MERV Rating

In 1987, the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) developed a Minimum Efficiency Reporting Value or MERV rating. Since they do not manufacture filters, the rating can be applied to all filters, including Filtrete and Hope Depot brand filters. The MERV rating is based on the gaps in the fibrous filter material. Since some particles are too large to enter the small gaps 100% of those particles are removed. With small gaps, some particles larger than the gap will be collected. MERV rating seeks to measure the amount of small particles trapped.

  • MERV ratings range between 1 and 20; the higher the number the smaller the gap and the higher the efficiency of the filter.
  • MERV-rated filters below 8 filter particles 10 and 3 microns.
  • MERV-rated filters between 8 and 14 are used in commercial and residential HVAC systems. They remove particles between 3 and 1 micron.
  • MERV-rated filters between 15 and 20 are designed for hospital and laboratory use. They remove particles as small as 0.3 microns—smaller than most bacteria and some viruses.

For comparison, human hairs are between 60 and 70 microns in diameter, common pollen is between 7 and 10 microns in diameter, spider silk is about 5 microns in diameter, and mold spores and bacteria are approximately 1 micron in diameter.

HEPA Filters

High-Efficiency Particulate Air filter is a designation by the Environmental Protection Agency for filters with gaps 0.3 microns or smaller. These filters collect and trap 99.97% of all airborne particles, including bacteria and viruses. HEPA filter applications include hospitals and laboratories but also are used in products that avoid allergic reactions.

It might seem appropriate to use the most efficient filter for health and safety. However, air filters with a MERV rating above MERV 14 are not appropriate for residential and commercial HVAC systems. Normal blower motors do not have adequate strength to push air through the extremely small gaps in highly efficient air filters. Consult with your HVAC professional before installing filters rated above MERV 14.

AC Maintenance Tips to Help with AC Filter Replacement are Just a Phone Call Away

Schedule your free AC Replacement consultation by calling AllCool AC & Heating at 281-238-9292 or contact us via email and let our NATE-certified HVAC technicians put their experience to work for you.