The SmartExhaust is a smart switch for controlling a bathroom exhaust fan. It has an adjustable delay feature allowing the fan to run for a period of time after the switch is turned off. It also keeps track of the total fan run time, and can be programmed to run automatically if necessary to meet ASHRAE 62.2 ventilation requirements.
Unlike the EFI switch, the SmartExhaust switch keeps track of total fan run time and operates the fan when necessary to meet mechanical ventilation requirements. In most cases, the switch should be programmed to meet the requirements of ASHRAE Standard 62.2.
Two parameters can be adjusted on the switch: the fan delay feature (0 to 60 minutes) and the ventilation feature (0 to 60 minutes per hour). To program the switch, it's necessary to know the effective airflow of the exhaust fan. Let's say you have a 100-cfm fan which, because of elbows in the fan's ductwork, has an effective airflow of 80 cfm. If your house needs 40 cfm of mechanical ventilation according to ASHRAE 62.2, the SmartExhaust switch should be programmed to run for 30 minutes each hour.
If the fan is programmed for a 15-minute delay, it will operate for 30 minutes if someone takes a 15-minute shower. In that case, no additional ventilation will be required for an hour. If no one enters the bathroom during the following hour, however, the switch will automatically turn on the fan for 30 minutes to meet ASHRAE 62.2 requirements.
The switch even includes a useful feature to override the programmed delay. If you are entering the bathroom for a short amount of time, and the fan delay feature is not needed, just "bounce" the switch on and off to override the fan delay.