What is the MERV Filter Rating System?
Understanding The MERV Rating System And How A Filter’s Rating May Impact Indoor Air Quality
What is MERV?
The coronavirus pandemic has heightened awareness and importance of the quality of the air we breathe. Ask yourself, how do you feel about returning to the office? As organizations continue to reopen and resume operations, confidence, trust, and a sense of security still varying. Whether you sit in a single office, have an open restaurant dining area, or a classroom filled with 20+ students, workplaces throughout the country must put air quality controls in place to help mitigate the risk of spreading viral contaminants and keep people safe.
To improve indoor air quality, the CDC recommends upgrading ventilation systems. However, upgrading an existing HVAC system is extremely costly. A more affordable option is to supplement air controls with portable air filtration systems, which can be used in any space. Regardless of the option chosen, the end goal is to ensure you have the suitable filtration needed to ensure the safety and well-being of your employees and customers with safe, clean air.
Most air filtration systems have a filter that helps capture harmful particulates and contaminants from the air. Not all air filters are equal in their efficiency, effectiveness or what they capture. To understand how your air filtration system cleans the air, you must understand the MERV rating of the filter inside the unit. MERV, also known as “Minimum Efficiency Reporting Value,” gauges what particles the filter captures from the air and its effectiveness in doing so. This blog covers the MERV rating system, what it means, and what you need to know when deciding what MERV rating your air filter should have.
What is MERV? Why Was It Created?
The MERV (Minimum Efficiency Reporting Value) rating system was developed by the American Society of Heating Refrigerating and Air Conditioning Engineers (ASHRAE), and is the industry-standard rating system utilized by ventilation and air filtration professionals nationally and internationally. The rating system helps determine a filters efficiency, effectiveness and what the air filter is able to capture and remove from the air. The ASHRAE, founded in 1894, focuses on “building systems, energy efficiency, indoor air quality, refrigeration and sustainability within the industry. Through research, standards writing, publishing and continuing education, ASHRAE shapes tomorrow’s building environment for today" (ASHRAE).
A filter's MERV rating is crucial to understand when determining what filtration level is the best fit for your workspace and needs. ASHRAE rates these air filters from MERV 1 to MERV 17, with MERV 1 being the lowest and MERV 17 highest. The rating assigned to a filter indicates the size and type of particles the filter can trap, such as dust, bacteria, viruses, gases, and other contaminants in the air. The higher the MERV rating, the smaller the particle size the filter can capture.
A MERV rating is determined based on laboratory testing results defined in the ANSI/ASHRAE Standard 52.2-2017. The ASHRAE report titled Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size explains that “the standard [52.2-2017] defines procedures for generating the aerosols required for conducting the test. The standard also provides a method for counting airborne particles of 0.30 to 10 μm in diameter upstream and downstream of the air-cleaning device to calculate removal efficiency by particle size” (ASHRAE Standing Standard Project Committee).
MERV Rating Chart
We created the below MERV Rating Chart as a reference guide to help understand how a filters MERV Rating correlates to effectiveness and what that filter captures. It is important to note that most filter's in commercial and industrial HVAC systems have a MERV 5-8. However, even if a filter is rated a MERV 8, additional filtration is needed to clean the air properly.
The EPA recommends, most indoor spaces that are non-healthcare related should have at least a MERV 13, to ensure proper filtration and clean air. The difference in the efficiency of a MERV 8 filter and MERV 13 filter is significant. A MERV 8 filter is approximately 20% efficient in capturing particles 1 µm to 3 µm, whereas a MERV 13 filter is at least 85% efficient at capturing particles of that size range, a 65% difference.
How Can A MERV Filter Help with Mitigating Spread of SARS-CoV-2 Virus (Covid-19)?
First and foremost, using the right filter and corresponding MERV Rating can help mitigate the spread of the SARS-CoV-2 virus within indoor spaces. ASHRAE has been frequently asked about the particle size of the SARS-CoV-2 virus and if air filters can capture it. According to the ASHRAE website, “Research has shown that the particle size of the SARS-CoV-2 virus is around 0.1 µm (micrometer)." However, the virus does not travel through the air by itself; the COVID-19 virus attaches itself to respiratory droplets and droplet nuclei (dried respiratory droplets) that are predominantly 1 µm in size and larger” (ASHRAE).
If you are looking to implement filtration controls to help mitigate the spread of the coronavirus in the air, you must use the correct filter with the proper rating. Referencing the MERV Rating Chart above, a filter with a MERV rating of 13 or higher can capture the SARS-CoV-2 virus particle size from the air. Note, the air filter can capture some of the viral particulates, which does not mean it completely removes the coronavirus from the air.
While protecting yourself and others from catching COVID-19 is essential, the need to improving indoor air quality predates the pandemic. We must not forget the other harmful contaminants and particulate in the air, leading to disease and illness that must be removed from the air. The right air purifier system, with an efficient filter, not only reduces the spread of COVID-19 but can remove other harmful contaminants from the air like bacteria, tobacco smoke, sneeze nuclei, and insecticide dust.
Whether you are a business owner, superintendent, or head of facilities, your number one priority is protecting your employees, customers, patrons, or students. If your employees do not feel safe and protected in their workplace, how do you think your customers will feel entering the establishment?
An Associate Professor of Exposure Assessment Science at the Harvard T.H. Chan School of Public Health and its Healthy Buildings Program, Joe Allen, is one of the leading researchers on this topic. The Healthy Buildings program is part of the Harvard T.H. Chan School of Public Health, which focuses on improving the indoor environmental quality of buildings, affecting people's daily lives. Allen has co-written various reports on indoor environment quality, such as The 9 Foundations of a Healthy Building and a book titled Healthy Buildings.
The book is an excellent resource for anyone who seeks to promote health and wellness by implementing strategies to improve the quality of their indoor environments. The Harvard Gazette published an article, How masks and buildings can be barriers to the coronavirus, where they interviewed Joe Allen. In the article, Allen discusses improving air quality for front-line institutions such as hospitals, nursing homes, grocery stores, etc. Allen says, “You want to make sure that if you are recirculating air, that it’s being filtered through upgraded filters." Allen also suggests that buildings have regular check-ups on their HVAC system to ensure that the filters are working correctly and airflow is not restricted. He makes the comparison of how you would not board a plane without a maintenance check. Why should an office building's ventilation system not be treated a similar way? The pilot of an aircraft is responsible for the safety of its crew members and its passengers. The same goes for the office building, school, or any indoor space.
CAUTION: Higher MERV Rating Is Not Always Better; It Can Restrict Airflow
Why would a higher MERV rating restrict airflow? Doesn't a higher MERV rating mean higher efficiency, so why would it be inefficient? For example, if you install an air filter with a high MERV rating and your HVAC system is not equipped to handle the increased resistance that the filter provides, it will restrict airflow, resulting in fewer air exchanges.
Even though a higher MERV rating means higher efficiency, it also means higher airflow resistance as these filters were designed to capture tiny particles from the airstream. In other words, installing too high an air filter would be like having too many chefs in a kitchen. Specific environments, such as hospitals, require a filter with a high MERV rating. But most indoor spaces do not need a filter above a MERV 13.
The consequences of restricted airflow can range from mild to severe. A benign outcome would be discomfort in the heating/cooling of the building. With the HVAC system not working at its optimal level, it will not effectively heat or cool every room in your building. A severe consequence would be your furnace heat exchange gets hotter from the restricted airflow and cracks. When that cracks, that can cause your duct system to release carbon monoxide. Now you have restricted airflow; the circulating have harmful contaminants.
There is no one-size-fits-all filtration indoor spaces since buildings, classrooms, office spaces, etc., come in different shapes, sizes, and uses. When assessing if you should upgrade your HVAC system or looking for a large-scale industrial air purifier system, consulting an HVAC engineer is highly recommended. HVAC engineers will be able to assess your ventilation system and assist you with installing the appropriate air filter for your office building. Also, the management of these buildings might need to rework how the office space is used to ensure optimal operational efficiency and safety.
The MERV Rating System is the best reference guide when choosing the right air purifier system and air filter. With the pandemic making us aware of the importance of indoor air quality, it is crucial to understand how the MERV rating of an air filter affects air quality and reduces harmful contaminants that can lead to disease and illness.
At Sanalife, our Indoor Air Quality Specialists work with individuals and organizations to help find the right portable air purifier solution with the optimal MERV rating based on the unique needs of the indoor space. Guidance from our team will provide you with peace of mind knowing you have the right resource to help protect your employees, customers, and students with the appropriate filtration for your needs.
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Allen, J. G., Bernstein, A., Cao, X., Eitland, E. S., Flanigan, S., Gokhale, M., . . . Yin, J. (2017). The 9 Foundations of a Healthy Building.
ASHRAE. (n.d.). About ASHRAE. From ASHRAE: https://www.ashrae.org/about
ASHRAE. (n.d.). Filteration and Disinfection FAQ.
ASHRAE Standing Standard Project Committee. (2017). Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size.
Grainger Editorial Staff. (2020, June 9). HVAC Strategies to Control Airborne Pathogens. From Grainger: https://www.grainger.com/know-how/business-operations/emergency-and-disaster-preparedness/kh-hvac-strategies-to-control-airborne-pathogens?cm_sp=CM-Con
Harvard T.H. Chan School of Public Health. (n.d.). Harvard T.H. Chan School of Public Health. From Harvard T.H. Chan School of Public Health: https://www.hsph.harvard.edu/
Harvard T.H. Chan School of Public Health. (n.d.). Home. From Joseph Allen's Faculty Website: https://www.hsph.harvard.edu/joseph-allen/
Harvard T.H. Chan School of Public Health. (n.d.). Joseph Allen's Faculty Website. From Healthy Buildings: https://www.hsph.harvard.edu/joseph-allen/healthy-buildings/
Healthline Wellness Team. (2019, April 16). Air Filters: Your Questions Answered. From Healthline: https://www.healthline.com/health/under-review-air-filters
Healthy Buildings. (n.d.). Healthy Buildings. From Healthy Buildings: https://forhealth.org/