Large Work-space Air Purifier features Filtrete air cleaning technology to help purify the air in your office. Designed for conference rooms or other large work spaces up to 320 square feet (16' x 20'). Three-stage filter design includes both Filtrete filter media and ionization for airborne particulate removal. Activated carbon filter for odor reduction and ionization removes smoke, dust, and pollen from air. Office Air Cleaner offers three fan speeds, ionizer on/off switch, and filter change reminder. Filter effectiveness lasts up to three months under normal conditions.