What is MERV rating on air filters?
MERV rating (or Minimum Efficiency Reporting Value) represents an air filter’s capability to capture or trap large particles measuring between 0.3 and 10 microns.
And what is a micron? A micron is a unit of length equal to one millionth of a metre (or one micrometre). However, micron has become the more commonly used term among the two.
So, you can imagine that when we say 10 microns, we’re talking about 1 metre divided 100,000 times. So, it’s still quite small. But in the particulate matter world, 10 microns is significant. Some airborne pollutants are as small as 0.1 microns in size.
Table of Contents
Who Came Up with MERV Rating?
MERV rating comes from the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). Since its formation in 1959, ASHRAE’s mission has been:
“advancing the arts and sciences of heating, ventilation, air conditioning and refrigeration to serve humanity and promote a sustainable world.”
Using some tests, the scientists came up with the MERV rating to compare the expected performance of different filters. MERV rating starts from 1 to 16, with MERV 16 filters the best at capturing particles.
The Complete Air Filter MERV Rating Chart
Below is a comparison chart showing the efficiency of different filters against particles of various sizes in microns:
|MERV||0.3 to 1 micron||1 to 3 microns||3 to 10 microns|
|1-4||not measured||not measured||less than 20%|
|5||not measured||not measured||20% or less|
|6||not measured||not measured||35% or less|
|7||not measured||not measured||50% or less|
|8||not measured||20% or less||70% or less|
|9||not measured||35% or less||75% or less|
|10||not measured||50 to 64.9%||80% or less|
|11||20% or less||65% or less||85% or less|
|12||35% or less||65 to 79.9%||90% or less|
|13||50% or less||85% or less||90% or less|
|14||75 to 84.9%||90% or less||95%|
|15||85 to 94.9%||90% or less||95% or less|
|16||95% or less||95% or less||95% or less|
Importance of MERV Rating in Air Filtration
MERV rating helps us to select the best filters for HVAC systems. As air comes in from the outside, air filters capture most particulates, thus ensuring that the indoor air is better for breathing. From the best performance, ASHRAE recommends that you install a MERV 13 filter.
However, if a MERV 13 filter cannot fit into your HVAC system, ensure that you buy one with the highest possible MERV rating.
Related Questions (FAQs)
These are some of the most frequently asked questions that are related to MERV rating in air filtration:
What is a HEPA filter?
A HEPA (or High Efficiency Particulate Air) filter is a type of filter that is common in vacuum cleaners and air purifiers. HEPA filters quickly capture up to 99.97% of tiny airborne particles measuring as small as 0.3 microns.
These include dust, mould, bacteria, pollen, and other allergens.
What is a True HEPA filter?
True HEPA filters are even more efficient than standard HEPA filters. They trap small airborne particles down to 0.1 microns. So, the efficiency is much higher at almost 99.99 percent.
Can HVAC system filters help with Covid-19?
The SARS-CoV-2 virus is around 0.1 microns. Therefore, it can pass through such filters. However, since the Covid-19 virus doesn’t travel alone but attaches itself to respiratory droplets, HVAC filters can help capture them.
ASHRAE recommends using a minimum MERV 13 filter or higher for the best results. However, you may want to complement such a filter with an air purifier with a HEPA or True HEPA filter for maximum performance.
Air filters capture most airborne pollutants as they pass through your HVAC system. However, not all filters work well. Thanks to the MERV rating, you can know the performance of different filters against particles of various sizes.
Unless a MERV 13 (or higher) filter cannot fit into your HVAC system, that is the best solution against particulate matter. Also, it would be best to combine such a filtration system with one of the best air purifiers in Canada for the best outcome.
Also, apart from ticking off activated carbon, remember to go through the other equally important criteria.