COVID-19 has presented numerous safety challenges to facility operations that has resulted in “new normal” best practices. Improved filtration is a cost-effective solution to improving HVAC operation and reducing virus transmission, but what is the right level of filtration for your HVAC system?  The answer depends on the equipment application.  We want to help operators make the best decision for their facility by answering some FAQs regarding filtration.

What is the recommend filtration level during COVID-19?

  • ASHRAE is currently recommending operators use a filter with a Minimum Efficiency Reporting Value (MERV) of 13, but a MERV 14 (or better) is more preferable.  Of course, the ultimate choice needs to take the capabilities of the HVAC systems into consideration.  Generally, increasing filter efficiency leads to increased pressure drop which can lead to reduced air flow through the HVAC system, more energy use for the fan to compensate for the increased resistance, or both. 
  • If a MERV 13 filter is not a viable option in the HVAC system, then use the highest MERV rating you can.

What is the particle size of the COVID-19 virus?

  • Research has shown that the particle size of the COVID-19 virus is around 0.1 µm (micrometer).  However, the virus does not travel through the air by itself.  Since it is human generated, the virus is trapped in respiratory droplets and droplet nuclei (dried respiratory droplets) that are predominantly 1 µm in size and larger.

What do the MERV filter ratings mean?

  • Filter performance is measured by the fraction of particles removed from air passing through a filter and is represented by a MERV rating (Minimum Efficiency Reporting Value). Filters are rated from MERV 1-16 with the higher number being the more efficient at filtering particulates.  See the table below for effectiveness against COVID size particulates.
Filter RatingEfficiency at capturing COVID sized particulates (1-3 micrometers)
MERV 1 – 7Not Effective
MERV 820%
MERV 935%
MERV 1050%
MERV 1165%
MERV 1280%
MERV 1385% (recommended)
MERV 1490%
MERV 1590%
MERV 1695%
*Represents MERV ratings per ASHRAE 52.2-2012

How often should HVAC filters be changed and replaced?

  • Filter replacement schedules do not need to be varied or increased due to the corona virus pandemic. Rather, schedules depend on how often filters load (pressure drop increases), which varies by location and run times of the unit. 

If you have any questions about the proper level of filtration for you HVAC system please reach out to BAS.