Points out that the US residential HVAC market still employs filtration methods from the 1930s created to protect the firebox of the hot air furnace and not an A/C coil. Resistance to change is fuelled by the lack of meaningful and understandable test methods for particulate filters, and the fact that most residential construction and HVAC equipment allow infiltration of unfiltered outdoor air. Focuses on a field study that demonstrates that enhanced central filtration can overcome the infiltration of unfiltered outdoor air and reduce particles generated inside the home. The study uses a new test method, ASHRAE Standard 52.2P, which establishes the minimum efficiency of particulate filters over a range of 12 size fractions, from 0.3 to 10 microns, over the full loading cycle of the filter.