I am making a homemade incubator and I was wondering if it really needs a fan? My bator is made out of an old 10 gallon fish tank, has a light, a water source, thermometer, hygrometer, shelf for the eggs to sit on, egg cartons for the eggs to sit in ect. Do I need to use this fan? I have one, but I am not sure if it is too big or not. What is the reason for having a fan? Will the eggs be fine with out it? The top of the fish tank is made of screen and I will put some sort of insulator on top of that but maybe if I keep some of it open will that be enough ventalation?