I put a 10 inch fan in mine. It's called Holmes accutemp heater, but it has a normal fan setting on it too. I use the heater when it gets cold in the winter like it is now and it snowed in my area not long ago so i set it to be at a constant 70 degrees. The lights heat it up to about 75 and then when the lights go out, the fan keeps it at 70.
good grow cabinet