Not a lot, but there is a lot of different types out now, mine is a full bodied one that holds a lot more heat in that a lot of these newer just reflector type. Some even have holes so the heat excapes up instead of down. I have seen a garden run 2 of the 8 bulb t5s in a 4x8x8 tall tent with just 2 6" duct booster fans to cool the whole thing, worked great for him.