This item is optional in warmer climates and can be installed to automatically switch on or off your Solar Whiz fan based on a user defined temperature. In cooler climates it prevents heat loss from your house and/or roof space in winter months. A manual on/off switch is a cheaper option of course but it requires someone to remember to turn it on or off.
Thermostat Controller SW1112
The Heat-Cool setting on the thermostat dictate when the fan will turn on. If set incorrectly, the thermostat will operate the Solar Whiz™ in the wrong way, turning it on when the roof space is cool and off when the roof space is hot. Have it set to either cool or off.