Your Guide to Air Filters
Using an air purifier can help reduce the amount of allergens and other impurities from the air you breathe, but while they may clear the air, the distinctions between different types of filters can be cloudy. From HEPA to carbon to ionizing, when you're not sure what even the words used to describe filters mean, it's no wonder that how they work remains a mystery. Filters all have the same goal - to reduce airborne particles - but how they accomplish that, and exactly what kind of particles they work on, can be very different from one device to another.
Starting at the top of the air purification pyramid is the High Efficiency Particulate Air filter. These are often considered the gold standard for air filters. To be certified as HEPA, a filter must be able to trap 99.7 percent of particles that measure 0.3 microns or larger. A 0.3-micron particle is far smaller than the width of a human hair and encompasses common impurities such as pet dander, dust and pollen. HEPA-type air purifier filters, such as the Holmes® True HEPA Filter, don't need to be made of a certain material as long as they meet filtering standards.
Carbon filters are another popular system, and they're primarily used to hold odors and vapors rather than allergen particles. A small amount of carbon can hold a tremendous amount of material, but the filter's effectiveness is based on its size. Since carbon traps the molecules that cause odors, all of the pores in the material will eventually fill up, and the filter will have to be replaced. Carbon filters are often used in conjunction with different types of filters to add odor-blocking capabilities.
Pre-filters can also be made from a variety of materials and some even contain activated carbon. These are used as a first-step filter to trap large impurities, such as pet hair, leaving the primary filter free to catch smaller particles.
Ionizing filters work not by trapping particles, but by forcing them to cling to another surface to get them out of the air. These filters produce a strong (but safe) electrical field for particles to pass through. Once electrically charged, these particles will be attracted to any surface with an opposite charge. Ionizing filters usually contain one positively charged surface and one negatively charged surface within them to capture as many particles as possible, but charged pollutants can even attract one another, making them too heavy to remain in the air.