Merv Rating – What You Should Know
What is a MERV Rating? (Minimum Efficiency Reporting Value)
The Minimum Efficiency Reporting Value, also known simply as MERV, measures the performance of air purifiers, specifically large purifiers intended to clean an entire house or building. Large, whole-house purifiers are not evaluated in the same manner used to measure the effectiveness of small, portable air cleaners, which are sometimes given Clean Air Delivery Ratings (CADR) instead.
Whole house and building air purifiers usually receive MERV ratings of between 1 and 16, but sometimes the upper limit is extended to 20. Common residential air purification systems tend to fall within a narrower range. Higher numbers translate to more effective air filtration. According to the online encyclopedia Wikipedia, “The scale is designed to represent the worst case performance of a filter when dealing with particles in the range of 0.3 to 10 micrometers.”
How is an Air Cleaner’s MERV Rating Determined?
Air cleaners are given MERV ratings based on the results of a series of tests. Simply put, the process works like this:
- Test particles are introduced into the air of the testing area. These particles fall into one of twelve categories, based on size. The smallest category contains particles ranging from .3 to .4 micrometers (also known as “microns”). The largest includes particles from 7 to 10 micrometers.
- The air is then passed through the filter being tested. The density of particles in the air is measured before and after the air passes through the filter to determine how effective the filter is at removing pollutants in each size category.
After this is done, the process is repeated five more times, so that there are ultimately six measurements for each of the twelve categories. The MERV number is assigned based on the worst result. Hence the “minimum” in “Minimum Efficiency Reporting Value.”
What Does an Air Cleaner’s MERV Rating Mean for You?
You might think that a higher MERV rating would automatically be better, but that’s not necessarily the case. The higher the MERV rating, the smaller the pores are for air to flow through an HVAC filter. This can create more resistance in airflow than a system is designed to manage, thus making it inefficient. Reducing the air flow in your system can actually worsen the air quality in your home and put a damaging amount of pressure on the fan of your furnace or AC system. So it is worth doing some research. Find out what the highest MERV rated filter is that still allows for maximum airflow in your system and be sure to change your AC filters regularly.