Problem is insufficient intake.
You should run a passive intake LOW in the room that is about twice the size of the active exhaust, or a couple passives. You can cover them with a flap that flaps inward when the fan is going to prevent light leaks.
stinkyattic Reviewed by stinkyattic on . Ventilation I have a 6' tall by 23"x24" cabinet. It has a 400w hps in it and a 449 CFM fan going to a cool tube then a ccfilter ccfilter--->cool tube--->fan something like that There is also a 4"x4" air intake with a computer fan blowing in. Still though tempratures rise into the 90s if the door is closed for an extended period of time. Since smell is an issue the ccfilter is necessary. Rating: 5