If your HVAC system does not have a filtration rating of more than 13 MERV, it is important to use as much outdoor air as the system can handle. Upgrading the unit's filtration to MERV 13 or higher is a step in the right direction, as it captures more particles than a typical MERV 8 filter. However, it is not as effective at trapping small particles the size of a virus, such as the coronavirus, which is 0.1 microns in size. A MERV 13 filter will only capture less than 75% of airborne particles that are 0.3-1.0 microns in size.
It is also difficult for many existing HVAC (heating, ventilation and air conditioning) systems to adopt a MERV 13 filter due to the increased load on the fan caused by the finer filter media. This can actually reduce airflow and cause more harm than good if the system is not designed to withstand that type of filter. On average, many installations are limited to one type of MERV 8 or MERV 9 filter. A HEPA filter is the ultimate solution in the world of air filters and far exceeds what a MERV 13 can do.
HEPA filters are the most efficient for residential or commercial use, followed by MERV 13-16 filters. These devices come with multiple filters to trap harmful particles and remove a large amount of COVID particles from indoor air. The problem is that a HEPA is a filter medium that is too fine to implement in existing HVAC systems and the only way to add one to an installation is through a portable or stand-alone HEPA air filtration system with its own dedicated fan designed to increase the resistance of this type of filter. More efficient filters cause a greater drop in pressure and your air treatment unit may not have sufficient capacity, explains Ray Charles, founder of Household Air.
However, the risks associated with handling filters or performing other maintenance activities within air conditioning systems potentially contaminated with coronavirus under conditions of use in the field have not been evaluated. One of their recommendations is to use air filters with at least a MERV 13 rating, or a higher HEPA rating when possible. These measures cannot be overlooked, even if you have the best air filtration and disinfection systems on the market. For even better results, filtering can be combined with an air purification method such as germicidal ultraviolet irradiation (UVGI). Because HEPA filters are so efficient, they cause a greater pressure drop than MERV-rated filters.
For a residential filter in a slightly loose slot, you can use a simple piece of tape, hold it in place and allow the air flow to push the filter forward to engage the flat surface in front. The professional opinion of an HVAC engineer is strongly recommended before attempting to upgrade any air filter. Considering the threat posed by the spread of COVID-19 and other germs, changing a building's air filter to a HEPA is much more effective than simply using a MERV 13 filter due to its small size (0.06 to 0.12 microns). The more efficient the filter, the better.