Staying Healthy

Can Air Filters Help Protect Your Family from The Flu?

Feb 10th, 2020

by Alec Lower

Studies suggest they can play a role in protecting your home from the flu.

Can Air Filters Help Protect Your Family from The Flu?

Studies suggest they can play a role in protecting your home from the flu.

by Alec Lower

We know that air filters help your indoor air quality. We know that they filter allergens like pollen and dust out of the air and that they protect your HVAC system from exposure to lots of crap that can cause breakdowns. But can air filters help fend off sicknesses as well?

Flu season is here, and you’re working hard to make sure nobody in your family catches the bug. Obviously, air filters aren’t going to make you immune, but can they filter pathogens like the flu virus out of the air? The answer may surprise you, or it might not, depending on how much you know about air filters.

The experiment

So can air filters actually decrease your chances of catching the flu? Well, yes, according to a recent study from the Illinois Institute of Technology. The study, which was prepared for NAFA by Dr. Brent Stephens of the aforementioned institution, set out to determine the effectiveness of HVAC filter filtration on the probability of an individual contracting infectious diseases. The study can be found here, but it’s a ton of reading with lots of words, so we’ll summarize it for you.

The experiment used a risk of transmission equation known as the Wells-Riley Model to test air filters of different MERV ratings and their respective ability to remove droplet nuclei from the air. What does any of that mean?

  • MERV: rating scale from 1-16 that grades the effectiveness of air filters. An 11 is solid.
  • Droplet nuclei: Droplets are little particles of moisture that you expel through your mouth and nose when you breathe or cough. These droplets contain particles within them, some of which are pathogens. As the moisture vapor evaporates, the particles within remain together suspended in the air. They form the droplet nucleus. This is commonly how airborne diseases get transmitted.
  • Wells-Riley Model: This is just a math equation used to determine the risk of infection based on a number of factors such as the number of infector individuals, exposure time, and other things.

Dr. Stephens used this model and some assumptions about the particle size of droplet nuclei to test the effectiveness of HVAC filters against these pathogen carrying particles and the subsequent effect on the risk of contraction. The tests were conducted in three hypothetical environments (offiice building, school, hospital) with three different infectious diseases per environment (Influenza, Rhinovirus, Tuberculosis).

The Results

The results of the experiment backed up the idea that increasing the MERV rating of your filter will result in decreased risk of contraction of the tested infectious diseases. The chart below illustrates the decreasing risk of Influenza in a school environment.

chart of contraction risk for influenza with increasing MERV

The chart illustrates that, if no filter at all is used, there is a 32.3% risk of contraction if one person with the flu spends eight hours at a school of 35 people. Eleven people would be expected to contract the flu virus based on this. It’s worth noting here that if you use a filter, but it is a garbage one like a MERV 4 or fiberglass, the risk level does decrease, but minimally.

However, opting for a MERV 13 filter cuts the risk level by about two-thirds, resulting in seven fewer people getting sick under the exact same circumstances. Below are the charts for Tuberculosis and Rhinovirus (common cold), which follow similar trends but with less risk in general, as they are less contagious diseases than Influenza. The trend holds true in the office and hospital setting also. You can see those charts here. charts for tb and rhinovirus

So should I use a better filter this flu season?

You should. Using a MERV 13 filter will not guarantee you immunity from the flu, but it will decrease the odds of you or a family member catching it in your home. MERV 13 filters, such as Second Nature’s Catch All filter, are about the most effective filters against small particles you can buy short of the HEPA variety. The experiment projects a MERV 13 filter will catch about 87% of droplet nuclei that pass through. A MERV 4 is only expected to catch 11%. So yes, you should opt for a better air filter.

How else should I avoid the flu?

Also, remember to get your flu shot and wash your hands frequently. Both of these are critical to fending off the flu. You can usually get the flu shot for $0 out of pocket at a local pharmacy. Surprisingly, doctors don’t put much stock into cleaning and disinfecting surfaces. The flu won’t live long on a surface like a countertop or a doorknob, so focus your energy on washing your hands and avoiding infected individuals.

Alec Lower
Alec Lower
Social Media and Content Specialist
After graduating from NC State, I joined Second Nature in the summer of 2018. I have always loved writing and enjoy blogging on subjects that are important to families and homeowners. Outside of work, I love to fish and am a huge college sports fan.