It depends on the size of your closet/room, plus what are you using to vent it. I started a 400W hps grow, my first grow, in a $25 plastic cabnet. 1'x2.5'x5.5'. i gutted it, and painted it black, then white to keep out/in light, and the white for reflection. then i took 3 cpu fans from my old comp, rigged them up to a 4v-12v ac/ adapter. 2 on top for exhaust, 1 on bottom, opposite side, anyways, with that setup, i never did keep my temps at 75-80F til i ended up running a duct from my window AC to my cab. then when the plants matured, they got too close to the lights and started suffereing. then i had to buy a air cooled hood with tempered glass between the light and plants. that did it. id do the same if possible, not really stealth in any way tho.