The unit has a 12v output for a fan that is contolled by the pit sensor. Set the temp and the controller does the rest, the temp drops and the fan comes on to stoke the coals. The temp goes above and the fan turns off. There are loads of setting that can be altered to affect how it functions. I only use it as a remote thermomter as it has 4 probes.
I got the fan from here: http://www.ebay.co.uk/itm/BBQ-Power-Dra ... 1494979262 A 10cfm 12v fan and adapter type A or C was $20 plus $15 shipping. I asked the question about just buying a fan. The fan housing has a damper built in so when the fan is off the damper stops air bleeding into the smoker.