need some advice on cooling fans? I built a canopy so i can vent hot air out a window behind my aquarium. I put two 8 inch fans in the window to suck hot air out which are rated at 250 cfm a piece. I figure i will need at least a couple blowing fresh air into the hood from the basement. I was looking at coralvue smart fans rated at something like 68 to 112 cfm, They are variable speed. Im gonna hook all of them to a thermostat.  should i just buy a fan that runs a constant speed or buy the smart fans which are the same price?