Air purifiers have been around in various forms since the 1940s, when the first HEPA filter was designed to protect workers from airborne nuclear material. Since then, air purifiers have been used in hospitals, work sites, and homes to protect against viruses, mold, bacteria, pollen, pet dander, tobacco smoke, dust mites, and a great number of industrial and household chemicals. The people who stand the most to gain from air purifiers are those with allergies, asthma, and other respiratory ailments.

But everybody can benefit from having cleaner air in the home. The Environmental Protection Agency lists indoor air pollution among the top five environmental risks to public health. In fact, the inside of your home could well contain two to one hundred times more air pollutants than an outdoor urban environment.

Air purifier value varies widely. You can spend upwards of $1600 for the best air purifiers known to man, or you can spend as little as $70 for a good car unit. You can also spend an arm and a leg on junk if you’re not careful. One thing to keep in mind when buying an air purifier is unit-to-filter value. If your unit uses a HEPA filter, find out how much it costs to replace the filter. You may end up spending thousands on the filter alone. The question is, what kind of a machine do you want?

Home air purifiers use a number of technological approaches to cleaning your air so you can breathe more easily. They use HEPA (High Efficiency Particulate Air) filters; electrostatic filters, ion generators, ozone generators, ultraviolet light, and other methods to get rid of both large and miniscule particles. Some operate by drawing in air via a fan, cleaning the air, and re-releasing it. Others work by actually sending out “purifying agents” throughout the room.

Today you have two basic choices for home air purifiers: room air purifiers, and whole house purifiers. Generally speaking, room purifiers are better for air-cleaning efficiency and cost.