I currently have a 90w led UFO and 2 65w(actual Watts) cfl in my tent. Current heat vents into the closet the tent is in and we leave the closet door open most of the time. we have to leave the door open regardless of where we vent our lighting as we live in the SE US and the closet will jump to 90 degrees in a few hours otherwise. My concern is that if I add a 400 w hid the vented heat will be too extreme. would I need to vent to the attic or would I be able to continue venting into the closet?
You will have to vent somewhere else. Even if it wasn't totally necessary though, it would still be a far better idea to do it anyways. You could possibly get away with it if you had the door open at all times and the air coming in from outside is cool air, but you would not be able to shut the closet door anytime the light was on, it would get way too hot.
You will have to vent if you add a HPS. I just ditched my 400w HPS for LEds but with my HPS it added 8-10 degrees of heat with a good cooling system. If your getting 90 degrees with your current set up HPS will push it to over 100. Almost guaranteed even with cooling most likely. You can never cool less then ambient unless you are using active cooling .... putting a AC in the room. That being said you will have to dramatically increase venting or move your grow out of your closet. Thats the downfall of closet grows...air exchange sucks.
Totally agree. I run my closet cabinet at nights and open the window when it gets to 70 degrees or lower outside for some active cooling. If I can't open the window, it approaches 90 degrees but there is nothing to do about it unless you run ducting to another room or outside. Even with the apartment A.C. it is not enough, venting to another room is a must if you add an HPS at those temps.