Used this metod http://www.heatsink-guide.com/conten...=control.shtml
and instead of connecting the wire to the pc fan i connected it to a relay that can be wired upto almost anything

All you have to do is get a thermometer and heater stand in your room and lets say you want it to kick in when temp hits 26'c then turn on the heater wait till temp hits 26 the turm the dial/ screw on the potentiometer untill it lets enough power through to trigger the relay and hay presto youve calberated it to 26'c so once your exaughst fan has expelled enough air and the temp drops down to 24 ish the relay will not be getting enough power and will shut off in return turning off the fan coool dont you think