Air Filtration: The Basics

Everyone can benefit from air filtration. All major metropolitan areas, and even many rural ones, have air quality problems that can affect otherwise healthy people. If you suffer from allergies, asthma or chemical sensitivity, it becomes even more important to have clean air.

While you can’t control the outside environment, you can control the air quality in our homes and offices. This includes the air that enters your home from outside, as well as pollutants that exist indoors such as dust mites, pet dander, outgassing from new building materials, and fumes from chemical-based cleaners.

Air treatment systems can be either filters, which use some type of filtration material; or purifiers, which treat the air using various types of technology and don’t use filter material. Some machines combine the two. The filter you choose will depend on your specific air quality problem; whether you have allergies or asthma; the size of the area you need to treat; and your budget.

Here’s a summary of some of the most common types of systems and what to look for when choosing a filter.

HEPA Filters
Most physicians who treat environmental and allergy problems agree that a HEPA filter is the most effective for these issues. HEPA (High Efficiency Particulate Arresting) is a filtration standard that requires the material to filter particles as small as .3 microns. In addition, to be considered true HEPA, it must remove 99.97% of these particles. HEPA material handles particulates such as pet dander, pollen, dust, dust mites and their parts, and tobacco smoke. Most of these filters combine HEPA material with a prefilter to remove larger particles, as well as an odor-absorbing material like carbon for chemical and gas fumes.

A few questions to ask when purchasing a HEPA air filter:

How many square feet of HEPA material is in the filter? The larger the material, the less often you’ll need to change the filter.

How efficient is the motor? This is measured in CFM, which is cubic feet per minute of air that can be moved. The CFM is an important factor in determining the area that can be effectively cleaned; the higher, the better. Make sure the manufacturer is not giving the rating of the motor itself; the number should reflect the air volume as it is exiting the filter.

How often do I have to change the filter? The best units have filters that will last from 3 to 5 years.

Electrostatic Filters
These machines create an electrostatic field to attract particles. Some use filter material (generally in the form of collection pads) and some do not. The former are the better choice because electrostatic units that don’t use filter material get clogged easily and need to be cleaned often. Units that use pads generally require monthly replacement. Electrostatic filters are not as effective as HEPA filters; they begin to lose their efficiency with particles smaller than 1 micron, so you may still need an additional point-of-use (POU) unit for a specific area of your home if you want to take out smaller particles. Electrostatics work on particulates such as pet dander, dust and tobacco smoke.

Central HVAC Filters
Also called whole-house filters or furnace filters, the typical HVAC unit is an electrostatic filter (see description above) that fits into the home’s central duct. These come in disposable and permanent versions. Disposables have a major disadvantage: They are made of Fiberglas^® or other types of spun glass that are not thick enough to work effectively; if they were dense enough to function as a barrier, they would restrict the air flow. Permanent filters are made of woven polypropylene, which does not restrict air flow. Permanent filters require that pads be changed, usually on a monthly basis.

While these units are effective for general filtration, they are not a substitute for periodic maintenance of the ductwork in central HVAC systems. Dirt and mold can still build up in the ducts, so regular maintenance is required.

Negative Ionizers
Ionizers generate negative ions to counteract pollutants, which are positive ions. The ions bind to particles, reversing their polarity so they drop to the nearest surface (floor, wall, etc.) or are neutralized. Although ionizers handle particles such as dust, pollen and cigarette smoke, they are not powerful enough for poor air-quality situations or for people with allergies and other health issues. Their added benefit of rebalancing the air ions has a beneficial effect on the body, so they are useful as a secondary device (in addition to a HEPA or whatever primary filter you choose). In addition, if your air quality is very good and you have no health problems, but you still want a fresher environment, an ionizer is a good choice. Ionizers have no filters to replace and can simply be dusted with a cloth.

Ozone Machines
This is probably the most controversial method of cleaning the air. Contrary to what many people think, not all ozone is harmful. Ozone is a gas produced when the sun’s ultraviolet rays contact our atmosphere. It is O_3, one oxygen molecule with an extra singular atom of oxygen attached. This gas cleans up pollution by oxidizing the pollutants, or breaking them down into their basic molecular components.

If you’ve ever walked into a hotel room and asked for an ozone machine to remove the smell of chemical cleaners, you were probably told to leave the room while the unit was on. That’s because hotels use machines that are more powerful so they can clean quickly. These units also contain a special type of plate to make the ozone; the plates emit nitrous oxide as a byproduct, and nitrous oxide can be harmful to the body and irritating to the lungs.

There are safe ways of making ozone, such as with an ultraviolet (UV) bulb. When used properly, ozone is very effective against chemicals, viruses, bacteria, mold and other pollutants. See the section below on UV Air Purifiers for more information on this technology.

Ultraviolet and Germicidal Air Purifiers
An ultraviolet (UV) bulb makes ozone (without nitrous oxides) at a certain wavelength—185 nanometers. This wavelength neutralizes odors and fumes from chemicals and gasses. When a UV bulb operates at 257 nanometers, it makes germicidal UV (also called UVC), a powerful pathogen killer that tackles airborne bacteria, viruses, mold and mildew. Some units use both UV and UVC wavelengths. These purifiers are the right choice for people who work in pathogen-laden environments such as hospitals; who are concerned about viruses and bacteria in general; or who have serious mold or odor problems in their environment. Some purifiers combine a UV bulb with a HEPA filter (see HEPA section above) for both particulate and germicidal protection. UV bulbs need to be replaced periodically.

Other Technologies
Additional purification methods that are unique to specific manufacturers include photocatalytic nanotechnology, in which tiny molecules of titanium dioxide (TiO2) are activated by an ultraviolet bulb, turning airborne pollutants into water and carbon dioxide; purifiers that emit non-ozone forms of oxygen which neutralize odors and pathogens; and non-UV germicidal units that apply a high-energy electrical field within a sealed filter compartment that traps and destroys micro-organisms.

No matter what type of filter you choose, remember to take stock of your particular situation so you have an idea of what you’re looking for before you start shopping.

Article by Cutting Edge