When it comes to protecting against the spread of COVID-19 and other germs, upgrading a building's air filter to a HEPA is a much more effective step than just a MERV 13. This is because viruses are incredibly small, ranging from 0.06-0.12 microns, and the more efficient the filter, the better. Filtering is a mechanical method of purifying air, which means it works with both living and non-living particles. HEPA filters are the most efficient for residential or commercial use, followed by MERV 13-16 filters.
However, these filters can cause a pressure drop due to restricted air flow, so the capacity of the ventilation system must be taken into account before using them. The figure below shows the starting points for intake air flows and cabin pressures for both types of filters, and then how the values decreased as the intake and final filters became dust-loaded. Figure 2 shows the PF determined for the closed cabs of the front drill and roof bolter, as well as the intake air flows with the MERV 16 filters and the HEPA filters. This compares to the PF for the roof bolter 77 to 1021 for the MERV 16 filters and 182 to 1425 for the HEPA filters.
The first point to note in the results is the extremely high comparison of the average PF values for the front drill and roof bolter with the MERV 16 filters and the HEPA filters. HEPA filters are much more efficient than MERV rated filters, but this comes at a cost - they have more resistance to airflow than MERV filters. The MERV rating of an air filter describes its efficiency in reducing particles from 0.3 to 10 microns in air passing through it. It's also important to note that there was an extreme amount of air leaking around the MERV intake air cleaner 16 through small cracks or gaps in the HVAC system.
This indicates that there were likely additional air leaks around other filters in the system. For smaller particles, filter fibers act as branches that trap harmful engine contaminants passing through them. With an air cleaner in a room, fewer contaminants reach the HVAC system filter, potentially extending its life and that of the system as a whole. This was seen in a test on a roof bolter, where there was a 3.2-fold increase in PF when comparing average post-month values to those with all new filters. Visual inspection of the HVAC system with removed filters showed dust deposits downstream of inlet and end filters, indicating multiple leaks around them. The purpose of MERV standards is to allow an apple-to-apple comparison of filtering efficiency between various air filters.
While MERV 16 filters are cheaper than HEPA filters and don't need to be changed as often, significantly reducing maintenance labor costs, HEPA filters are still more effective at capturing small particles.