NEWEST ADVANCED PERFORMANCE VALUE-3 FILTER Regular Size (19.5 x 18.75 x 1.75) Genuine Pureatech System Economy Filter Pack. Includes: 4 - ADVANCED PERFORMANCE combination Particulate & Gas Phase Filters in one. Note Filters include Proprietary Medias that can be used with or without the UVC Germicidal Bulb. Effectively Captures Fine Particulate Matter...Inhibits Microbials...Removes Toxins, Gasses, Chemicals & Odors (Converts Ozone / Smog into Oxygen)...with ONE ALL PERFORMANCE FILTER. Recommend: For Maximum Performance & Efficiency Use Two Filters & Change the combination Filter(s) every 90 days. Especially recommended when dust, allergens and smog levels are elevated.For Single Filter Use - Place the APV3 Filter in the Stage Three Slot.