I am a clean air fanatic, trained in the nuclear field and a sufferer of COPD, need I day more. Air entering our home is filtered and the forced air furnace runs full time for air filtration. The large filters are for the garage window fan, so I can work in clean air. Its amazing how many particulate contaminates this filter catches, especially during the fire season, California smoke this year. Clean air is an exciting subject for me.Thanks for your high quality filters and prompt service.