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Posted on December 10, 2020

While COVID-19 spreads mostly through close personal contact, some evidence suggests it can become airborne and travel long distances in certain situations. That means managing air purification in interior spaces is an important part of public health.

Building managers should know how HVAC systems can aid in reducing airborne contamination to keep employees and customers safe as people transition back into normal life in 2021. This can lead to better preparedness for other types of contaminants and diseases in the future, as well.

Today, we’ll look at different types of airborne contaminants and how HVAC systems can improve infection control and indoor air quality. Filtration, ventilation, and disinfection through techniques like UV radiation and ionization can all play a part.

What Are Airborne Contaminants? 

On a basic level, we can think about two types of airborne contaminants: natural and man-made. Pathogens like viruses and bacteria fall into the first category, as well as pollen and mold. Man-made contaminants include chemical vapors, gases, and smog particles.

Different techniques of air purification have varying degrees of effectiveness. For example, filters with a minimum efficiency reporting value (MERV) of 8 can capture pet dander and pollen. MERV 11 filters can capture mold spores and smog, while MERV 13 filters can capture tobacco smoke, bacteria, and viruses.

CDC and ASHRAE Statements on COVID-19 in Interior Spaces

The CDC has stated:

“COVID-19 (SARS-CoV-2) can sometimes be spread by airborne transmission. Some infections can be spread by exposure to viruses in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than six feet away from the person who is infected or after that person has left the space.”

ASHRAE’s position is:

“Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures. Neither WHO nor CDC rule out the possibility of aerosol transmission under some circumstances and both recommend the use of engineering controls in some cases….”

How HVAC Technology Can Help in Reducing Airborne Pathogens

Ventilation systems can help reduce air pollutants and microorganisms with a range of techniques including filtration, ventilation, humidity control, UV lighting, and ionization. Let’s take a look at each of these in detail.


Air filters are rated for efficiency at removing particles of different sizes, and MERV ratings of 13 or 14 are recommended by ASHRAE for HVAC systems in buildings. MERV 14 may not be sustainable for some standard air handling units or rooftop units, and MERV 15 and 16 cause excess strain.

The most penetrating particle size is 0.3 microns. Particles above this size are easier to trap by filtration. Counterintuitively, particles smaller than 0.3 microns are also easier to trap. SARS-CoV-2 particles have diameters between 0.06 and 0.14 microns, which means they are easier to trap than 0.3-micron particles. MERV 13 filters capture up to 75% of 0.3-micron particles, so they are more than 75% effective at trapping coronaviruses and similar-sized viruses.

HEPA filters are the most efficient in purifying contaminated air. These filters can trap over 99% of 0.3-micron particles, but they also put more strain on an HVAC system. That’s why HEPA filters are usually only used in hospital environments and other healthcare settings.

When switching to a higher filtration efficiency, you can schedule an HVAC inspection to make sure your system can handle the increased pressure drop. If the system can’t handle a MERV 13 filter, it would be better to choose a lower filter than risk creating other problems like stagnant air or differences in room pressures.

Airflow and Ventilation

Good airflow does a lot to reduce contaminants. The CDC recommends buildings open outdoor dampers as high as 100% to allow the maximum amount of fresh air, though this can be hard to achieve if it’s extremely hot or cold outside. Here are a few more tips for airflow:

  • Circulate air in rooms but don’t point a vent directly at a person’s desk or cubicle. If a sick person sits under a strong vent, their respiratory droplets can spread farther.
  • Consider running the HVAC system at maximum outside air flow for two hours before and after occupied times.
  • Similarly, increasing air changes per hour (ACH) can lower the risk of spreading diseases in a work or school environment.
  • Open windows whenever possible.

Maximizing ventilation is important, but there’s a balance between that goal and energy efficiency. Taking in 100% fresh air without recirculation requires more energy from the HVAC system since it needs to condition all of it. A solution is to use an energy recovery ventilator (ERV).

A thermal wheel in an ERV rotates between intake and exhaust air streams. The wheel transfers the temperature and relative humidity of the conditioned exhaust air stream to the intake air, and vice versa. If warm, humid air is coming in, the ERV trades its energy and humidity for the conditioned air’s lower temperature and humidity.

The system transfers energy while keeping air streams separate. It allows the HVAC system to save energy without recirculating indoor air that could have picked up viral contaminants from people inside the building.


Pre-pandemic, a commercial building with relative humidity between 20% and 60% was acceptable. However, there are higher infection risks with humidity below 40%. Lower humidity allows viruses to survive longer and reduces some of the body’s natural respiratory defenses. ASHRAE now recommends building environments be kept between 40% and 60% humidity. Above that range, other issues like bacteria, fungi, and mites can develop.

UV-C Lights

UV-C lights can be used in ductwork to neutralize pathogens in moving air and also on wet surfaces like evaporator coils. UV LEDs exist but are not nearly as effective as traditional lamps. Here are a few different applications:

  • In-duct UV to disinfect air: High doses of UV from multiple lights can reduce airborne pathogens in HVAC ductwork. The irradiance zone needs to be at least two feet long for this technique to be effective on moving air.
  • In-duct UV to disinfect surfaces: UV lights directed at coils and drain pans can reduce bacteria growth and improve air quality. Since the goal is to target areas with condensation, fewer lights are needed, and they can run 24/7.
  • Upper room UV: Rooms with higher ceilings can have UV lights installed that irradiate the area above seven feet. The upper air is constantly disinfected, and this translates into many additional air circulations per hour.

Technicians can also use portable UV light units to decontaminate specific rooms to contain an outbreak.


Bipolar ionization has been used in healthcare settings for years, and it was effective at reducing the SARS virus in 2004. The process creates ions out of oxygen which attach themselves to microparticles, bacteria, and viruses.

The ions are over 99% effective at deactivating a virus’ ability to infect a victim. And when ions attach to droplets and other microparticles, the particles increase in size so they can be filtered more easily. Ionization technology has improved in recent years, and the cost of installing a unit has gone down. It’s also effective for reducing allergens, odors, mold, and smoke.


Ozone is a reactive gas that kills bacteria and viruses. Ozone can be used for disinfection of unoccupied spaces if it’s handled properly by a professional cleaning company. But it’s generally ineffective for continuous use in HVAC systems if kept to public health standard levels.

Find Out if Your HVAC is Efficiently Purifying the Air

During this time, it’s important to use the right technologies to keep people safe at work. Optimal solutions enable your HVAC system to reduce contaminants in a way that conserves the most energy.

If you’re in the process of increasing your system’s purification ability, reach out to an HVAC specialist at Wm. T. Spaeder to assess energy efficiency and determine the best control solutions. Our team specializes in a range of industries in the Erie, Pittsburgh, and Buffalo areas.


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