Filters with a MERV-13 rating or higher can effectively protect against the spread of Covid-19. MERV-13 is the minimum filter rating recommended by experts for HVAC design work. This rating ensures that at least 90% of particles in the 3-10 µm range, 85% of particles in the 1-3 µm range, and 50% of particles in the 0.3-1 µm range are removed. But how can someone looking for an oven filter at their local store determine the filter's rating? Is there a Merv number printed on the filter? MERV stands for Minimum Efficiency Report Values and is a test method developed by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). Therefore, using a high-merv filter to purify the air of COVID-19 can certainly help reduce its spread in an office environment.
These types of filters are more commonly found in hospitals and laboratories, as they are necessary for sterile environments. If you want to filter the air in your home to improve indoor air quality and potentially eliminate any coronavirus particles, you need to know what particle size to filter and what type of filters will do it. Alternatively, you can upgrade your ventilation system to be suitable for at least Merv 13 filters. However, these filters are expensive, scarce, and can cause poor performance and damage to units not designed for that increased pressure drop.
It's important to note that 90 percent of the time it doesn't matter what filter you have installed, since air doesn't pass through it. Therefore, it's better to use a lower MERV filter correctly than a higher MERV filter that is misused. To get the best results, filtering should be combined with an air purification method such as ultraviolet germicidal irradiation (UVGI). When you start to climb up to MERV 8 or higher, you start to see some potential health benefits, although many of them depend on context and how it's used.
The test procedure for merv classification uses 6 measurements and 12 particle sizes, resulting in a total of 72 data points. Filters are primarily there to protect equipment: keep coils clean, fans clean, and ducts free from large chunks of dust.