I have one 120mm(4") low speed Vantec Stealth computer fan in each end of my 100G fully enclosed canopy, each blowing in with equal sized exit holes in the roof of the canopy placed towards the center and over the reflectors/fixtures so the air has to travel up and over the lights and carry the heat out. They are powered by variable voltage DC power supplies (wall warts) like you use to charge cell phones or DC appliances. The variable voltage allows me to vary the speed accordin to the cooling needs. Each Vantec moves 53 CFM so I get about 10 air changes a minute inside the canopy at 12v and they are very quiet due to the low speed.