You maintain social distancing. You wear a mask. You wash your hands. You disinfect high-contact surfaces. In short, you follow all the CDC recommendations to keep yourself safe from COVID-19.

…or do you?

Recently, the CDC recommended that schools, businesses, and homes install MERV 13 filters. According to the CDC, MERV 13 filters provide the best protection against COVID-19.

What are MERV 13 filters? How do they work to protect your home and family? Read on to learn more about the best COVID-19 filters.

What Do Air Filters Do?

The air inside any building contains natural pollutants. These include dust, dander, mold spores, and other allergens and microorganisms. In addition to heating and cooling the air, a building’s HVAC system works to remove these natural pollutants.

Air filters are responsible for this work. As air circulates indoors, it eventually passes through the HVAC system’s air filters. When it does, filters are designed to catch dust particles, allergens, and other microorganisms. The result is cleaner and healthier air in indoor spaces.

What Does an Air Filter’s MERV Rating Mean?

Air filters are rated according to their ability to filter out various particles.

A filter’s MERV rating describes its minimum efficiency reporting value. Simply put, a filter’s MERV rating tells you what size particles that filter can trap.

Filters with lower MERV ratings offer less resistance. These filters will trap bigger particles. However, they will allow smaller particles to pass through. Filters with higher MERV ratings offer more resistance. This means that filters with higher MERV ratings will trap more and smaller particles.

Particle size is measured in microns. One micron equals 1/25,000 of an inch, or one-millionth of a meter.

The following list shows different MERV ratings and their corresponding ability to trap air particles.

  • MERV 1-4 filters can trap particles larger than 10.0 microns
  • MERV 5-8 filters can trap particles between 3.0 and 10.0 microns
  • MERV 9-12 filters can trap particles between 1.0 and 3.0 microns
  • MERV 13-16 filters can trap particles between 0.3 and 1.0 microns
  • MERV 17-20 filters can trap particles smaller than 0.3 microns

Before the COVID pandemic, most residential and commercial HVAC systems used air filters with low to moderate MERV ratings. EPA recommendations identified MERV 8 filters as the minimum acceptable for indoor air quality.

People who struggled with allergies and those with compromised immune systems sometimes used filters with higher MERV ratings. Still, filters with a rating of 13-16 were generally reserved for hospitals, smoking lounges, and other buildings where air filtration needs were highest.

In August, however, the CDC revised information regarding the coronavirus and how it spreads. In revising its understanding of the virus, the CDC also revised its recommendations for air filters.

How Does the Coronavirus Spread? Understanding Droplet and Aerosol Transmission

As its name suggests, the novel coronavirus is new. Because the virus is new, experts’ understanding of it is evolving. Research continues regarding the ways COVID-19 is transmitted.

Droplet Transmission

Early in the pandemic, experts believed that the coronavirus spread primarily via droplets. When people talk, cough, sneeze, and even breathe, they expel droplets of saliva. These relatively large droplets are also relatively heavy. Therefore, they fall quickly to the ground and other surfaces—usually within a few feet.

If they originated in the mouth or nose of a person infected with COVID-19, these droplets can contain the virus.

When a healthy person stands close enough to a sick person, he or she can come in direct contact with these droplets and the virus. If a healthy person touches a surface where the droplets fell, he or she can likewise become infected.

Social distancing, masking, hand-washing, and disinfecting aim to reduce this type of transmission.

Aerosol Transmission

Recently, the CDC updated its understanding of coronavirus transmission to include the possibility of short-range aerosol transmission. Aerosols are tinier particles, or “droplet nuclei.” Because they are smaller, they can remain suspended in the air for longer periods of time.

To risk infection via this mode of transmission, a person need not stand close to someone who is infected. Rather, a person could simply walk through a space an infected person had previously occupied. If the aerosol particles remain in the air, a healthy person could inhale them and become infected.

The amount of time aerosol particles remain in the air depends on a variety of factors. These include the size of the particles and the quality of ventilation in the space.

Virus particles are generally smaller than 1 micron in diameter. According to the CDC, particles that are 1 micron in diameter and smaller can remain suspended in the air for up to 12 hours. Particles smaller than 0.5 microns can remain in the air for up to 41 hours.

These estimates describe the time it takes for aerosols to settle on their own. However, proper air ventilation can remove these tiny disease-causing particles much more quickly.

Why Is MERV 13 the Best Filter for Coronavirus?

To offer protection against the coronavirus, an air filter needs to provide enough resistance to capture tiny aerosol particles.

In fact, MERV 13 filters are rated to remove particles that are between 0.3 and 1.0 microns. This range includes the average size of most virus-containing aerosols, including the coronavirus. Filters below MERV 11 offer no protection against particles of this size. Even MERV 11 and 12 filters only remove a fraction of the smallest virus-containing aerosols.

When you purchase a MERV 13 filter, however, you can rest assured that it will filter:

  • More than 50% of particles between 0.3 and 1.0 microns
  • More than 85% of particles between 1.0 and 3.0 microns
  • More than 90% of particles between 3.0 and 10.0 microns

Thus, MERV 13 filters offer the best protection against aerosol transmission of the coronavirus.

Can I Simply Replace My Existing Air Filter with a MERV 13 Filter?

MERV 13 filters offer superior protection against the airborne transmission of the coronavirus. However, you do need to exercise caution when adding MERV 13 filters to your arsenal of COVID defenses. This is because some HVAC systems are not designed to use such powerful filters.

Air filters become more effective at trapping particles as their resistance to airflow increases. Increasing resistance can thus be a good thing when you’re aiming to remove harmful particles from the air.

However, increasing resistance to airflow also makes your HVAC system work harder to circulate the air. If your HVAC system isn’t designed to handle this increased resistance, you can wind up with more problems.

As airflow decreases, the overall efficiency of your HVAC system can decrease as well. In turn, your system may struggle to heat and cool the air. If the system experiences enough strain, damage to the compressor or heat exchanger can result.

It’s necessary, therefore, to check the manual for the manufacturer’s specifications on the MERV ratings your system can handle.

If My HVAC System Can’t Handle a MERV 13 Filter, How Else Can I Enjoy MERV 13 Protection?

If you find that your HVAC system isn’t rated to handle a MERV 13 filter, you may still be able to use a MERV 13 filter in your home or business. Many people have experimented with creating their own air purifiers by attaching a MERV 13 filter to a box fan.

The process of making a DIY air purifier is simple and cost-effective.

  1. Purchase a MERV 13 filter and a standard 20-inch box fan.
  2. Apply a perimeter seal or weatherstripping to the edges of the air intake side of the fan.
  3. Use tape or rubber bands to secure the MERV 13 filter to the air intake side of the fan.
  4. Turn the fan on, and you have your own MERV 13 air purifier for less than $50.

What Else Can I Do To Protect Myself from Airborne Transmission of the Coronavirus?

Because uncertainty remains about how the coronavirus spreads, the best prevention strategies target transmission via droplets and aerosols.

In addition to using MERV 13 filters, you can also reduce the risk of aerosol transmission by increasing the circulation of outdoor air in indoor spaces.

First, open windows and doors—and utilize cross-ventilation—as much as possible.

If your HVAC system has one, open the outdoor air intake damper. Also use the heat or energy-recovery ventilator if your HVAC system has one. If your system doesn’t have these features, you can still increase ventilation by setting the system’s fan to run even when it is not heating and cooling.

Keeping your furnace filters clean is another important step toward improving air quality and your HVAC system’s efficiency.

Use a portable evaporative cooler or air purifier if possible. The minimal effort required to fabricate a DIY MERV 13 air purifier is well worth the protection it provides.

Finally, to protect yourself from droplet transmission, remember to follow CDC guidelines. Social distancing, masking, handwashing, and disinfecting remain among the best ways to protect yourself and others.

Use MERV 13 Filters and Leave COVID-19 Out in the Cold This Winter

As winter approaches, you’ll likely spend more time indoors. The air quality in these indoor spaces affects your health under ordinary circumstances. During a pandemic, indoor air quality becomes even more important.

If your system can handle it, a MERV 13 filter provides the best protection against indoor airborne transmission of the coronavirus. You can also create your own MERV 13 air purifier using a box fan. Finally, you should continue to follow CDC guidelines.

As you take the steps you can to protect yourself and others, count on the experts at American Fabric Filter. Contact us with your questions today.