Lennox X8349 Maintenance Kit for PCO-12C PureAir Air Cleaner. MAINTENANCE KIT INCLUDES: (1) MERV 10 pleated filter model X6664 (1) Catalyst Insert – Model 75X73 (new 1″ design)  (4) UV Lamps Model X8149 (Formerly 10M35) Replace metal insert and lamps every 24 months. Replace insert more frequently if you notice a significant drop in odor removal efficiency. If you find that you need to replace the  insert more frequently than every 24 months, consider source reduction and/or ventilation to reduce the levels of contaminants in your home Note: DO NOT WASH metal insert. Washing will destroy the titanium dioxide catalyst that coats the insert surface.