As we all practice social distancing and stay at home during the COVID-19 pandemic, many are wondering what else they can do to help “flatten the curve”. While hand washing and staying at home remain the most effective means of limiting the spread of the virus, conflicting information emerges about the role and effectiveness of air filters. Can air filtration in a building protect us from COVID-19?Filtration in building heating, ventilation and air conditioning (HVAC) systems may be part of an overall risk mitigation approach, but it is not generally considered a solution in itself. There is no direct scientific evidence of benefit, but reduced exposure can reasonably be inferred based on the ability of some filters to remove particles containing the SARS-CoV-2 virus.
For filters to have any impact on the transmission of infectious diseases, transmission must occur through the airway, filters must be properly installed and maintained in systems suitable for treating recirculated air, and filters must be designed appropriately for the building in which they are used. Hospitals (and many healthcare facilities) have specially designed mechanical systems that can be adapted to the filtration levels they need. They are often based on other control systems and strategies (for example, isolation of known cases and hand washing). However, none of these technologies have been shown to reduce infection in real buildings, even if they show promise based on tests conducted in a laboratory or in an idealized environment. Portable air filters may also be used as part of an overall risk mitigation approach. 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, as it generally does not address transmission by surface contact or by close contact between people. However, DNA and RNA from other viruses have been found in filters used, which are usually associated with droplets. When changing filters, it is advisable to assume that they contain microbiological active material. It is not known whether this represents a significant risk of infectious virus disease, but the precautionary principle suggests that care should be taken. This becomes particularly important in any building (including a home) where infectious diseases, including COVID-19, are known or likely. With the recommendation of a MERV 13 or higher filter, does a MERV 13 meet your needs? A MERV 13 filter is a step in the right direction and captures more particulates than a typical MERV 8 filter.
However, it is not as good at capturing small particles the size of a virus as a HEPA can. A MERV 13 will trap less than 75% of air particles that are 0.3 to 1.0 micron in size (coronavirus is 0.1 micron). It is also difficult for many existing HVAC systems to adopt a MERV 13 due to the increased load on the fan by the finer filter media. On average, many installations are limited to one type of filter MERV 8 or MERV 9.MERV 16 is the tallest filter you can buy, but your air conditioning system may not be able to handle it. A possible target benchmark for good ventilation is CO2 readings below 800 parts per million (ppm).
If baseline readings are above this level, re-evaluate the ability to increase outdoor air supply. In conclusion, while air filtration may be part of an overall risk mitigation approach for COVID-19, it is not generally considered a solution in itself. Hospitals have specially designed mechanical systems that can be adapted to the filtration levels they need and portable air filters may also be used as part of an overall risk mitigation approach. With the recommendation of a MERV 13 or higher filter, does a MERV 13 meet your needs? A MERV 13 filter is a step in the right direction and captures more particulates than a typical MERV 8 filter but it is not as good at capturing small particles the size of a virus as a HEPA can.
