Found this very helpful and a cheap alternative to thermostats
i modfied it and instead of conectin it to a pc fan i wired it to a relay that powers a bigger inline fan
I just mentioned that the schematic will only drive up to 12V, but yea dc fans are fine to overpower, the caps in them are often rated for 50V I've noticed.. If the sensor can handle higher voltage, you could just hook it up to a higher supply.. If its touchy, just add a resistor..