101 CFM Fan Metal Halide Cooling Fan Pictured to the left are the fans I use to cool my Metal Halide lights. These are AC fans which are rated for 101 CFM. (Cubic Feet per Minute). They are 4" inch square fans which are mounted to the side of the lights blowing over the bulbs They come with chrome finger gaurds if you need them. Since I have an open top hood, I do not have fans blowing in or out of the hood. If I had a closed hood, I would have both fans blowing inwards.