4 1000w in a 8x8 area in a square will require in my opinion an 8" vortex fan ducted with a y joint to the two lines of two hoods. U will also need passive intake from a cool air source or a AC unit (inside grow room, but u will still need fresh air flow). Put 1 carbon filter per string of lights at the opposite end of the room from your air intake, using the 8" fan to pull air from the grow room through the filters over the lights and out of the room. This will remove the heat and filter the air, but this method requires u to be bringing in cool air, or air conditioning inside the grow room and only running the exhaust when the lights build up too much heat, which also brings in fresh air.