The air diffusion performance index (ADPI) concept and its implementation in the diffuser selection guideline (ASHRAE Handbook-Fundamentals, 2009) provide designers a simple method to design overhead-air-distribution systems. However, the current guideline considers only five diffuser types and the range of sensible cooling loads used to develop the guideline (65 W/m(2)-250 W/m(2)) is high for current buildings. Applying this outdated guideline may cause draft discomfort and/or unnecessary fan-energy waste. This paper presents new experimental results to update the ADPI-based guideline to include 15 diffuser types at low cooling loads of 25 W/m(2) and 50 W/m(2). Compared to the high loads in the current guideline, the ADPI values generated in this work are greater due to the lower loads used. Most ceiling mounted diffusers produce higher ADPI at a large range of airflow than do sidewall and other diffuser types. ADPI for ceiling diffusers has the least variation with changes in loads or airflow rates. The results show that the minimum airflow set-point for a variable air volume system varies with diffuser type. For ceiling diffusers other than round and perforated diffusers, the minimum set-point can be reduced to lower than 30% of the peak flow rate without significantly reducing ADPI. (C) 2016 Elsevier B.V. All rights reserved.