That would be alot of heat. If you had the ballast on the outside of the box and ran wires into it that would help to reduce your heat and I believe would remove the "fire hazard" risk.

Get a small fan and mount it on one side of the box like an exhaust fan on the topside of one side and bore out a nice size hole on the other lower side. That would definately help!

Good luck with the grow!:thumbsup:
Psycho4Bud Reviewed by Psycho4Bud on . IS THIS HAZARDOUS? Hi all just outta intrest would a 400w hps lamp with ballast be ok to run in a cupboard about 2 1/2foot x 2 1/2foot square and about 10foot high? or would it just cause too much heat? and be a fire hazard? Rating: 5