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MERV Filter Ratings - What Are MERV Ratings?

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What Are MERV Ratings? - Furnace Filter Ratings

There are a few different ways filter manufacturers rate the efficiency and effectiveness of their furnace and air conditioning filters. These main ways are regarded as the MERV, FPR, and MPR filter rating systems. In this article, we’d like to define and discuss the MERV filter rating system, and then tell you a little about how we rate our filters.

What Does MERV Stand For? What is a MERV Filter Rating?

‘MERV’ stands for Minimum Efficiency Reporting Value, and it’s a rating scale meant to measure the effectiveness of air filters. Originally developed in 1987 by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), MERV ratings are measured by the minimum particle size (μm) against the typical controlled contaminant and the typical application. MERV ratings are rated on a numerical scale ranging from 1 to 16. MERV ratings are based on ASHRAE Standard 52.2.

Here is a rough breakdown of how MERV ratings work (keep in mind, though, that it’s not an exact science):

  • MERV rating 1 – 4: Between > 10.0 μm (particle size). Application example: Residential window air conditioning units
    • Filter is able to filter out contaminants such as pollen, dust, and carpet fibers
  • MERV rating 5 – 8: Between 10.0–3.0 μm. Application example: Middle-grade residential units, as well as low-grade units inside general commercial and industrial workplaces
    • Filter is able to filter out contaminants such as pet dander, dust, mold, and hair spray
  • MERV rating 9 – 12: 3.0–1.0 μm. Application example: Top-grade residential units, middle-grade commercial and industrial units
    • Filter is able to filter out dust from humidifiers and dust, milled flour, emissions from automobiles
  • MERV rating 13 – 16: 1.0–0.3 μm. Application example: Top-grade commercial and industrial units, such as hospitals
    • Filter is able to filter out bacteria, cooking oil, smoke, paint
  • MERV rating 17 – 20: < 0.3 μm. Application example: Top-grade commercial and industrial, such as electronics and pharmaceutical manufacturing
    • Filter is able to filter out viruses, salt, smoke

According to ASHRAE, medium-efficiency (middle grade) filters with a rating of MERV 7 – 13 are almost as effective with reducing allergens in the air as HEPA (High-Efficiency Particulate Arrestance) filters.

Our Filter Ratings

At Purity, we don’t rate our filters. It’s not because we don’t believe in our filters; it’s quite the contrary. We believe that while MERV ratings can give a decent overview for the effectiveness of a filter, it isn’t an exact science. It doesn’t cover the lifetime efficiency of a filter, and it isn’t anywhere close to a perfect rating system. And, we do believe such ratings can be unreliable by nature.

Also, many times, filter manufacturers will test and rate their own filters, which we also do not believe in. We believe that all testing should be done by a third party that is removed from the situation.



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