Filter Types

There is really no sense in having a conversation about air cleaners if you aren’t already familiar with some of the terms used to describe the different parts of air purifiers. By parts, I don’t mean things like motors and fans – those are pretty self-explanatory. What we are talking about here are the different filtering and germ-killing systems used to clean your air. Let’s get an idea of how well each of the purifier types work.

As its name should tell you, this filter is usually the first stage that air passes through as it goes through your purifier. It will catch large particles floating around in the air, such as hair and clumps of dust.

Charcoal and Activated Carbon Filters
Simply different names for the same thing, charcoal and carbon filters use natural elements to capture and neutralizes odors. Sometimes, charcoal /carbon is added to the pre-filter to create a two-in-one filter.

True HEPA Filters
A true HEPA filter is one that removes up to 99.97% of allergens and irritants 0.3 microns and larger. For more information about how HEPA filters work and the impact they can have on health, visit WebMD.

HEPA-Type Filters
HEPA-type filters are constructed in a similar fashion to true HEPA filters, but are a little less effective. Some trap 95% of allergens and irritants 0.3 microns and larger, while others are only able to nab irritants 0.7 microns and larger.

Ultraviolet Germicidal Irradiation (UVGI)
Also sometimes called UV-C, this type of purification uses UV light to kill germs. Since it does not actually use any sort of a filter and, thus, cannot trap larger irritants such as allergens, the U.S. Environmental Protection Agency (EPA) suggest using it alongside a mechanical filtration system such as a HEPA filter.

Ozone Generator
This type of purification system is rarely used in a home setting. It uses ozone to kill off viruses and bacteria and to nullify toxic gasses. Since it releases strong, potentially dangerous amounts of ozone into the room, it is usually used only in extreme cases and only when a room is completely unoccupied. You will not find any reviews of this type of purifier on this page.

An ionizer works somewhat like an ozone generator, but on a smaller scale. Instead of inundating a room with ozone, it creates small amounts of ozone inside the unit and passes the air through this charged space which alters the electrical patterns in the irritants, making them less harmful.

Since very little ozone is released from these machines they are generally considered safe for regular use in the home, though this is still a topic of debate. However, a detailed study from the National Institutes of Health revealed that “exposure to negative or positive air ions does not appear to play an appreciable role in respiratory function.”

For more information on how ionizers work, check out this E-How article.

PlasmaWave Technology
This type of air purification uses an electric pulse to attack bacteria, viruses, and chemicals in the air. Since it creates both positive and negative ions at the same time, it does not create ozone. To read more about this type of technology, visit the Winix website.

Air Purification Terminology

Let’s get a basic idea of commonly used air purifier terminology. You may already know some of these terms, but others could seem completely foreign.

CADR Ratings
You are bound to come across this term in your search for an air purifier. In fact, I’ve used it quite a few times on this website myself. CADR ratings measure the clean air delivery rate, a measure of efficiency. It tells you how quickly a purifier can remove certain irritants from the air – the higher the numbers, the faster the purifier filters the air. Often you will find that units have different ratings for different irritants, such as pollen, dander, and smoke.

CADR ratings

More information about CADR ratings can be found on the website of the Association of Home Appliance Manufacturers.

The delivered airflow, as measured by ACH (Air Changes per Hour) or CFM (Cubic Feet per Minute), describes the maximum amount of air that can be moved. It’s not a direct measure of cleaning capacity, although it often relates to CARD.

The contaminants most people treat with air purifiers are bacteria, mold, viruses, and airborne allergen particles such as smoke, pollen, dust mites, and pet dander. Some air purifiers also treat odors and gasses, but smells can come from all sorts of molecules so it’s important to know the type of chemicals you’re treating to determine whether or not your air purifier can clean them.

I talked about microns a lot in our brief discussion on true HEPA and HEPA-type filters. If you aren’t familiar with this term, you are probably wondering how big of a difference there is between 0.3 microns and 0.7 microns. It’s is actually quite substantial in the world of allergens and pollutants. A human hair is equal to about 90 microns – we’re talking about diameter here. A single dust particle is as large as 10 microns. Pet dander and pollen are usually around 5 microns. Smoke particles and germs are 1 micron or less in size.