WhisperGreen Select™ multi-speed with time delay allows you to select the proper cfm settings to satisfy ASHRAE 62.2 continuous ventilation requirements. The fan runs continuously at a preset lower level (0, 30 to 100 or 0, 50 to 120 cfm, in 10 cfm increments), then elevates to a maximum level of operation (50-80-110 or 110-130-150 cfm) when the wall switch is turned on or when the motion sensor or condensation sensor module is activated. A high low delay timer returns the fan to the preset cfm level after a period of time set by the user. Applies to both the pre-installed multi-speed with time delay, as well as the FV-VS15VK1 multi-speed with time delay plug 'N play module.