The use of an underfloor plenum to deliver conditioned air directly into an occupied zone of a building is a key feature distinguishing underfloor-air-distribution (UFAD) systems from conventional ducted overhead systems. Current research (www.cbe.berkeley.edu/underfloorair) and design practices are focusing on two plenum-related topics that can have significant impacts on the successful operation of UFAD systems:

- Air leakage from pressurized plenums.

- Underfloor-plenum-supply-air heat gain (thermal decay)

This article will present updated design and operating guidelines addressing both of these topics.