A 400HPS is not a lot of electricity considering that a TV or computer draws about that many watts.
You will have to consider removing heat from the space though. The lamp and exhaust should be considered a single entity- the size exhaust you need depends on the light and space. An open closet door only works during veg. During flower, you need too have a way to exchange air without allowing light to enter the space.
Consider buying a replacement closet door and modifying it for your purposes, and replacing the original closet door when you prepare to move out of the apartment.
stinkyattic Reviewed by stinkyattic on . 400w to much for apartment? Im gonna be doing my first grow in my apartment closet but i was wondering if i should Go with a 250w or 400w hps/mh combo. Would the 400w be suspicious? And how much heat do these bulbs really produce, i have a pretty open closet and dont know if i need to invest in an air coolable system or even go with a 4 bulb T5 system supplemented with 4 cfl's on the side during flowering?. Rating: 5