Not entirely a newby but...

[JohnM99]

Also, about MH and heat - it is not the ballasts at all - it is the bulbs. They run an internal temperature of something like 1100 degrees compared to 170 for fluorescents (numbers may be a bit off, but you get the idea).

MH lights need good venting and fans or open tops. A fan is also a good idea over a closed canpopy anyway for O2 exchange. T5 lights are a bit hot but nothing like MH - and they consume a LOT less electricity. Most MH hoods have a built in fan.