Minimum Efficiency Report Value (MERV) ratings measure a filter's ability to capture particulate matter. Filters with MERV-13 ratings or higher can trap smaller particles, including viruses. Many home HVAC systems come with a MERV-8 filter installed by default. Yes, most public health guidelines suggest that transmission of COVID-19 is predominantly associated with large droplets.
This is why air filtration is only a small part of a solution, since it generally does not address transmission by contact with the surface or by close contact between people. However, the distinction between droplets and particles in the air is the size of the particles. We know that droplets can remain in the air for long periods of time, and DNA and RNA from other viruses, which are generally associated with droplets, have been found in the filters used. The COVID-19 virus attaches to droplets that are released when a person coughs or sneezes. These atomized particles range in size from 1 to 100 microns, so any filter with a MERV 9 rating or better would be effective at trapping them.
With the recommendation of a MERV 13 or higher, does a MERV 13 filter meet your needs? A MERV 13 filter is a step in the right direction and captures more particles than a typical MERV 8 filter. However, it's not as good at capturing small virus-sized particles as a HEPA can. A MERV 13 will trap less than 75% of air particles that are 0.3-1.0 microns in size (coronavirus is 0.1 microns). It is also difficult for many existing HVAC (HVAC) systems to adopt a MERV 13 because of the greater fan load of finer filter media, which can actually cause more harm than good and reduce airflow if your system is not designed to handle that type of filter. On average, many installations are limited to one Merv 8 or MERV 9 filter type. To help protect against the COVID-19 virus, ASHRAE changed its recommendation from MERV 8 filters to MERV 13+.
RP Fedder sells a full range of MERV 13+ filters and can help you determine what types of filters and efficiency ratings you need. In general, filters with a MERV 16 rating or lower are considered HVAC system grade filters for residential, commercial, and general hospital use. With a portable air purifier through Sanalife, you can access easy-to-use air filtration systems with Merv 13+ ratings. MERV 17 to MERV 20 filters are commonly used in operating rooms, cleanrooms, and other settings that require absolute cleanliness. MERV 13 and above can be used as a final filter in cleanrooms, operating rooms, inpatient hospital care, and smoking rooms.
MERV ratings 1 to 4 are generally only used as pre-filters, but can be found in many typical applications, such as commercial buildings, ovens, and window air conditioning units. Because HEPA filters are so efficient, they cause a greater pressure drop than MERV-rated filters. MERV 17 to 20 will also capture virus carriers, carbon dust, combustion smoke, radon progeny and microscopic allergens (particles of size 0.3 micron).MERV 14 and higher can capture particles that are even smaller than previous MERV ratings, ranging from 0.3 to 1.0 microns in size. While there is no standard merv rating recommended for reopening during the COVID-19 pandemic, ASHRAE recommends a MERV rating of 13+, which is designed to capture 1 micron sized particles that would be effective for capturing COVID-19 virus particles indoors.
MERV 16 is the tallest filter you can buy, but your air conditioning system may not be able to handle it. The following table summarizes the average stop and applications of filters along the MERV scale, and the typical particle size for which they are used. In general, finding a filter with a higher MERV rating will correlate with greater efficiency in capturing particles and contaminants in the air. It's important to note that MERV and HEPA are two different types of air filters, although you've probably seen both related to air filtration. One of their recommendations is to use air cleaners with at least a MERV 13 rating, or a higher HEPA rating when possible. Using an air filter with a MERV rating higher than recommended by the manufacturer of your oven or air conditioner may impair its performance. In conclusion, while an HVAC system with an installed MERV 8 filter may not be able to completely stop viruses from entering your home or business space due to its limited efficiency level compared to higher rated filters such as MERV 13+, it still provides some level of protection against airborne contaminants.