The Complete Guide to Air Filters

From sizes to types to qualities and more, here is everything you could ever need to know about air filters.

The world would look different without air filters. Air wouldn’t be as clean, HVAC systems would be blowing up all over the place, and I, the author, would be unemployed.

Thankfully, we have air filters, though, and if you’re new to the world of air filtration, you’ve come to the right place. Here at Second Nature, we’re not experts in a lot of things. We don’t know anything about movies, nobody here can teach you quantum physics, and the meaning of life is still a mystery to us too, but air filters? We’ve got that.

What is an air filter?

An air filter is a semi-permeable shield that stands between your HVAC system and the air inside your home. It looks like this:

air filter on white background

What does it do?

It filters air. As your HVAC system pulls air from your home to cool or warm it, the filter intercepts that air in your ductwork. It acts as a barrier for anything carried by the air that you don’t want in your home. This includes things like dust, mold spores, pollen grains, pet dander, and a bunch more junk. That stuff gets caught by the filter and clean air moves on without it.

Why do I need one?

Because Indoor Air Quality is an increasingly significant problem in the United States. According to the EPA, the air inside your house can be significantly more polluted than the air immediately outside. This is because of the concentration of pollutant sources and the fact that air can stagnate inside a sealed building. An air filter helps remove pollutants and particles that would otherwise freely float about inside your home.

Not only does this make the air you breath most often cleaner and safer, which promotes personal health and home wellness, but it also keeps gunk from reaching your HVAC system. HVAC breakdowns can occur because of particle buildup on the actual coils of the system, and breakdowns are costly to fix (assuming they can be fixed at all). We can all agree that being without A/C in the winter or summer sure would suck.

Yes, A/C is used to heat and cool your home. It stands for Air Conditioning. It’s quite literally conditioning your air to be warmer or cooler. You’re welcome.

So I just buy one and leave it in there?

Nah, you got to change that filter. A filter will eventually fill up with gunk and become less permeable, allowing less air through and forcing your HVAC to work harder. This can, at best, drive your power bill up and, at worst, burn out the motor, which again will cost you thousands. Second Nature recommends using a pleated air filter (you can read more about what that is below) and changing it every three months. As stated by the Department of Energy, this will keep your HVAC system running smoothly and can actually lower your power bill by 5–15%.

Oh, and did we mention the health benefits?

So what does this all get me? Well, a healthier home for starters, which in turn delivers a healthier you. Filters catch allergy inducing pollutants like pollen and dust, but they also catch pathogens like bacteria if you’re using a sufficient quality filter. According to a NAFA Foundation Report, a filter with a high MERV rating can significantly reduce the risk of contracting infectious diseases such as influenza, rhinovirus (common cold), and tuberculosis. According to the study, upgrading from a MERV 4 filter to a MERV 13 filter can cut the risk of contracting influenza almost in half. Just from using a different air filter. So pick a quality filter and get started protecting the air in your home.

Have more questions? We’ve got lots more answers:

More filter basics:

Types and varieties:

Filter ratings:

Extra stuff:

Alec Lower

Content Writer

Alec is a third-year member of the team at Second Nature. He brings expert knowledge of a myriad of home air filtration topics including HVAC filters, filtration efficiency, and indoor air quality.