Remember, it's a freezer, so the thermostat will probably give you 10 deg at 1 and -10 at the max setting. I set mine around 4. The controller takes over, it won't work any harder if you set the thermostat higher as the air temp inside will never get below 20 or so (if you have a fan in there). The inside temp can get pretty cold if you have 80 deg beer in there and are trying to cool to 50 or so for lager pitching. Having a fan inside will make the beer cool quicker and keep the inside temp more even. I usually put a thermowell in one of two carboys to maintain the beer temp.