True, halides are a b1tch for heat. I got up to 90 with my 2X250s on my 75. And that was with the glass tops, with them off it only got to 86. With the chiller it hangs out at 78. I build my canopy completely enclosed, no open back, and 2 fans (one in and one out) if you are doing pendants or a hanging fixture its going to be less severe than mine, but with the tops heat will get trapped in pretty bad, and cause temps to rise too high.