Make sure your intake is at least 6 inch round pipe.Then at least 2 4 inch exhaust outlets.The more flex you use the less cfm's you will have. That fan will create a negative pressure.If you don't replace that air with fresh, the fans will never shut off. Don't matter what your thermometer is set at.You have to replace the amount of air you exhaust,in equal parts or it won't work.It will be an inferno in there.I run 600's and they get hot.

Ga Grown!:jointsmile: