How Are MERV Ratings Determined in Canada?

Because the pathogen that causes the COVID-19 disease is spread via a respiratory transmission (i.e., breathing in the infected respiratory droplets from someone carrying the virus), businesses and governments have employed air filtration strategies to help combat the spread of the disease. 

But how do you know if an air filter works well enough to help prevent the spread of COVID-19, or to address other air filtration concerns such as eliminating common allergens from the air? Reliable air filtration manufacturers will use a MERV rating to indicate how effective their filters are. Some jurisdictions in Canada and the United States have even gone as far as mandating certain MERV ratings for public spaces to be able to reopen. 

In this article, air quality experts from Camfil Canada explain MERV ratings, what MERV means, and how MERV ratings are determined. 

MERV Acronym Meaning — What Does MERV Stand For?

The acronym MERV stands for “minimum efficiency reporting value.” In other words, MERV ratings are a way of indicating how efficient an air filter is at capturing particles of various sizes.

MERV ratings are represented by a number ranging from 1 to 16, with MERV-16 providing the most protection and MERV-1 providing the least. 

The following table shows the efficiency of each MERV rating against various particle sizes. 

In general, the higher a filter’s MERV rating, the better that filter will be at trapping specific kinds of particles at first use. However, it is important to note that the efficiency of many air filters quickly deteriorates, meaning that the factory-tested MERV rating may last as little as a month, leaving you less protected after that point. 

For a filter that maintains its rated efficiency across its entire life cycle, look for a MERV-A-rated filter.

How Are MERV Ratings Determined in Canada?

MERV ratings are verified through a series of standardized factory tests, which are determined by ASHRAE. The tests involve adding particles of varying known sizes to the airstream in a controlled environment. Particles are counted both upstream and downstream of the filter to determine  how many particles are being trapped in the filter media. This test is repeated six times, and the lowest (least effective) value is then used to calculate the filter’s MERV value. By using the lowest number of particles captured, the MERV rating represents a worst-case scenario, so each filter is guaranteed to be at least as effective as its MERV value. 

Every type and efficiency of air filter should have an individual factory test available to ensure that it is delivering the level of efficiency advertised on the label. What Does MERV-A Mean?

A filter with a MERV-A rating has undergone additional tests to show that it will maintain its rated efficiency for its entire life cycle. Particulate air filters work by trapping particles within the filter media. Generally speaking, the more fine fibers in a given area of filter media, the higher the particle capture efficiency on smaller particles.  

The space provided in HVAC systems places major restrictions on the proper type of filter to be used (panel filter, bag filter, box filter, etc.). As a result, many manufacturers use an electrostatically-charged panel filter to artificially increase the efficiency of their filters. This keeps  the filter depth at a minimum so  the one-, two- or four-inch filter can fit in standard residential and commercial HVAC systems. However, the downside of using charged media is once the charge dissipates, the filter’s efficiency is reduced greatly. This can occur within a month of installation, or less with a heavy dust load and high humidity.

A MERV-13 panel air filter, for example, may only be as effective as a MERV 9 or even a MERV 8 filter once its electrostatic charge dissipates. 

MERV-A-rated filters, however, are tested after any electrostatic charge has been removed through a conditioning step. Therefore, the MERV-A value of the air filter represents its lifetime efficiency. 

Related: Property and Facility Management Air Filtration Guide

What is the Difference Between MERV and HEPA?

 HEPA air filters are distinctly different from MERV-rated filters and HEPA filter classifications are determined by a completely different set of factory tests. 

HEPA stands for “high-efficiency particulate air” filter.  Actual HEPA filters are the most effective air filtration devices that modern technology can provide, filtering out a minimum of 99.97% of particles at 0.3 micron.

However, many products are incorrectly marketed as HEPA filters, particularly with the rise in demand for HEPA filtration due to the excellent protection it provides against airborne pathogens. As with MERV-rated filters, be certain that the manufacturer of any HEPA air filtration equipment you purchase is able to provide the factory testing paperwork to back up the product’s advertised efficiency. 

Related: Should I Use an Antimicrobial Filter for COVID-19? 

What MERV Rating Should I Use for COVID-19 in Canada? 

The higher the efficiency of an air filter, the better protection it will provide against COVID-19 and other airborne pathogens, such as various strains of influenza. Most of the panel air filters that come with HVAC systems only filter enough dust and other particulate matter out of the air to prevent the HVAC equipment from being damaged, but are not efficient enough to protect human lungs from contaminants, including pathogens. 

As per the official recommendations of ASHRAE, as well as many other notable organizations such as the WHO, a MERV-13 air filter was determined to provide adequate protection against COVID-19 for public applications such as schools, office buildings, and other commercial buildings. To ensure that building inhabitants are protected for the entire life cycle of the filter, use a filter tested and labeled as MERV-13A or higher if your HVAC system has sufficient space to do so. 

Camfil Canada recommends using the highest MERV-A rated filter your HVAC system can house without impeding airflow and supplementing with in-room air purifiers that use HEPA filtration (with factory certification test provided)  particularly in high traffic areas. 

To learn more about the best air filtration solutions for your building, reach out to your local Camfil Canada representative

About Camfil Canada Clean Air Solutions 

For more than half a century, Camfil has been helping people breathe cleaner air. As a leading manufacturer of premium clean air solutions, we provide commercial and industrial systems for air filtration and air pollution control that improve worker and equipment productivity, minimize energy use, and benefit human health and the environment. We firmly believe that the best solutions for our customers are the best solutions for our planet, too. That’s why every step of the way – from design to delivery and across the product life cycle – we consider the impact of what we do on people and on the world around us. Through a fresh approach to problem-solving, innovative design, precise process control, and a strong customer focus we aim to conserve more, use less and find better ways – so we can all breathe easier. 

The Camfil Group is headquartered in Stockholm, Sweden, and has 31 manufacturing sites, six R&D centers, local sales offices in 30 countries, and about 5,200 employees and growing. We proudly serve and support customers in a wide variety of industries and in communities across the world. To discover how Camfil Canada can help you to protect people, processes, and the environment, visit us at


Media Contact: 

Berni Baier 

Camfil Canada Inc. 

T: (905) 660-0688 


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