HEPA filters have a fine 0.3 micron mesh that can filter most pollutants and allergens in the air, but are not capable of filtering out smoke, fumes and odors. They are noisier but often more effective than other air purifiers. Carbon filters are made from activated carbon and are very effective at removing odors, smoke and fumes. HEPA and carbon filters are often combined because they complement each other.

Ionic air purifiers contain electrostatically charged plates that attract particles in the air. These are good at removing pollutants of any size but don't work on odors. Ionic air purifiers are also the quietest models to run. There is a risk of ozone gas getting into the air when using this type of air purifier. Ozone should not be breathed in as it may cause lung damage.

Ozone filters are effective at removing odors and they also carry the risk of ozone contamination.

Ultraviolet light air purifiers kill off the microbes in the air with ultraviolet light; they don't filter out any pollutants.

Before purchasing consider the how much air the machine is capable of cleaning in a given amount of time and what size of room you will be using it for. For smaller rooms a lower capacity is fine. For a house be sure to get a machine capable of handling the air space.

Consider the maintenance the machine requires. Many require regular filter changes or cleaning. Get a good warranty to save money on repairs and replacements.

• Hamilton Beach
• Honeywell
• Rabbit Air
• Ionic Pro
• Hunter
• Ion-Care
• 3M