Originally Posted by BCtrippin

http://www.controlwizardproducts.com...php?prod=EL500

Buy yourself one of these. Best investment Ever. They are fairly cheap too. Its a cooling thermostat. You plug your fan into the thermostat, and set the thermo to the temp you want. When it reaches that temp, the thermostat kicks in power and your exhaust fans turn on.

Seeing that you would be paying for c02, your not going to want to run your exhaust all day and lose the c02. Set up your exhaust on a cooling thermometer and it will only kick it when it gets too hot.