DYSON HP04 PURE HOT + COOL HEATER FAN AIR PURIFIER - FOR PARTS OR NOT WORKING. Key Benefits of the DYSON HP04 Pure Hot + Cool Heater Fan Air Purifier Advanced Air Purification: The DYSON HP04 features a powerful HEPA filter that captures 99.97% of allergens and pollutants as small as 0.3 microns, providing you with clean and fresh indoor air.