The coronavirus pandemic has put a spotlight on the importance of indoor air quality. COVID-19 super spreader events” tend to take place in situations where multiple people are inside room with poor ventilation for an extended periodEssentially, the solutions to this problem all revolve around reducing the concentration of living virus in the air. There are several things that can be done in combination for an effective defense against the airborne spread of coronavirus, from masking and social distancing, to opening windows, to HVAC system modifications, to the addition of devices that sanitize the air. In that final category, the undisputed king of air sanitation is HEPA (High Efficiency Particulate Air) filtration. 

HEPA Explained 

HEPA isn’t so much a type of filter as it is a rating of filter. To qualify as a True HEPA filter, it has to be able to capture at least 99.97% of 0.3 micron (aka “micrometers”, millionths of a meter) particles from the air that flows through it. To put this into perspective, the smallest dust particles you can see drifting in the air in the sunlight from a window are around 10 microns. The famous N95 mask is so named because it is capable of filtering out at least 95% of 0.3 micron particles. The reason 0.3 microns is the particle size used for these ratings is that it is close to the most difficult size of particle to filterParticles smaller than this tend to move around erratically, getting caught in the process0.3 micron particles tend to be very good at riding air currents, drifting smoothly with the flow of air between filter fibers. 

HEPA Filters vs. Coronavirus 

Viral particles of SARS-CoV-2 are about 0.12 microns, and can ride saliva or dust aerosol particles that are much larger. The whole size range of potential viral aerosol is efficiently captured by a HEPA filter, and even moreso by Medical Grade HEPA filters, which are tested and rated down to 0.1 microns. This is all to say that any air that passes through a True HEPA air purifier gets pretty darn clean before it comes out. 

Shopping for HEPA Filters

There’s a few things to evaluate and look out for:

  • Beware of gimmicky UV and ionizing air purifiers, which do not have the proven efficacy of HEPA purifiers, and can produce trace amounts of ozone (despite misleading claims) that may build up over time in areas of poor air circulation, causing respiratory irritation.  Look for a “True HEPA” unit.


  • The market is full of air sanitation or purifying devices with marketing that focuses on how quiet they are. This is a big red flag. A large air filter on a low setting can be pretty quiet while still filtering significant volumes of air, but even with a quiet fan, there should be a whisper of white noise from the sound of the air moving through the machine. Pay attention to the CFM (Cubic Feet per Minute) or CADR (Clean Air Delivery Rate) of the device, and be suspicious when these are hard to find. The CFM rating of the fan (with no filters) will be higher than either the CFM of filtered air or the CADR. Once you know the airflow through the filter, you can use room dimensions to calculate ACH (Air Changes per Hour) for different rooms using this equation:

ACH = (CFM X 60min/hr) / (LXWXH of room in feet) 

The number of air changes per hour recommended for a particular type of room or building depends on the activities in that space. Consider running portable HEPA units in any indoor space that has more than one occupant from different households, especially when the volume of air in the room is relatively small.

HealthMate HEPA Filter ACH
The ACH of a HEPA unit can vary drastically depending on the speed setting and size of the room.
  • Consider the maintenance involved and how often pre-filters and/or the HEPA filter must be replaced.  While a unit may appear low cost, maintenance costs can add up with some units. You’ll only get the clean, purified air while the filters can properly capture particles.


Azenity Labs is a distributor for high-quality HEPA air purifiers, like the medical-grade Austin Air HealthMate. We have affordable options for sale and leasein addition to IAQ (Indoor Air Quality) testing. Call for a free assessment, and we can offer professional advice on how HEPA units can most effectively be utilized in your business or school. 

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