High efficiency filters (i.e. MERV 13 or equivalent, and higher) installed in a residential air handler with sufficient runtime can effectively reduce the concentration of airborne particles in homes. However, many central systems don’t have sufficient runtime, and high efficiency filters often have a high pressure drop that can negatively impact HVAC system performance. Explore the fundamentals and lessons learned to date from research on high efficiency air filtration, including the ROCIS Air Handler/High MERV filter Inquiry (http://ROCIS.org). In ROCIS, over forty air handler systems have been tested to determine if they should be used with a high MERV filter to affordably reduce household particle levels. It was found that in 90% of the cases, existing problems should be addressed prior to increasing the system’s runtime with a high performance filter. Additionally, experimental measurements of in-situ particle removal efficiency of over 50 residential filters in a test facility at the Illinois Institute of Technology offer insights into how filters perform in removing PM2.5 and ultrafine particles (smaller than 0.3 micrometers).