Determining which air purifier is best for your situation can be overwhelming with literally hundreds of different types available on the market. But deciding what features you need and comparing units with the same features will make the choice much easier. Here are answers to 6 of the most frequently asked questions about how to rate air purifiers.

1. Does the number of filters in a cleaner really make a difference? A cleaner without a filter or with one filter will require much more maintenance and filter replacement than one with multiple filters. Absolutely, the more filters a cleaner has, the more effective it will be.

See if it contains pre-filters. These filters are great at trapping fairly large particles that you can see (such as hair and dust) and prevent tiny particle filters from becoming unnecessarily clogged quickly. For best results, large and medium particle pre-filters are recommended.

2. What type of filter is best for removing particles? High-efficiency particulate arrest filters (abbreviated as HEPA) are the most effective at removing particulates. This is the same technology that hospitals use to keep the air clean. By definition, this type of filter must be able to remove 99,997 out of 10,000 airborne particles of 0.3 microns or larger. And a micron is defined as one millionth of a meter.

This type of filtration is recommended for those who suffer from allergies caused by airborne irritants such as dust, dust mites, mold and mildew spores, pet dander, and seasonal pollen.

3. Which filter is most effective at removing gases, chemicals, and odors? In a word, carbon has proven to be the best at absorbing gaseous pollutants. A carbon-based filter with additives that target things like the chemicals in nail salons or the smell of urine in kennels can really clean the air of these noxious odors.

4. Is a cleaner that uses low ozone levels safe? The United States Environmental Protection Agency (EPA) has ruled that any amount of ozone produced is unsafe. And the state of California has banned the production of ozone-producing cleaners.

5. How often should the filter be changed? The ideal purifier has a combination of filters that can effectively purify the air and still not need to be replaced for years. With the right combination of filters, your cleaner should be able to last at least 5 years without filter replacement.

6. How many hours a day must the unit run? A unit with a split capacitor motor will allow your cleaner to be on duty 24 hours a day. This will continually keep pollutant levels low and indoor air quality high.

Being able to remove pollutants from the air is what an air purifier should do. Choosing one that scores highly in each of these categories will ensure that you bring home one that works well for you.