The least expensive way of reducing the heat in the grow room is to vent out the heat and replace it with cooler air. The best way to setup a venting system like this is to mount one exhaust blower on the inside of the grow room up high to blow the heat out, and another blower on the outside mounted down low blowing cool air in.
Hot air rises, cool air settles.
This is the amount of air the blower will move in one minute without any restrictions on the intake or exhaust. Aluminum tubing with smooth inside walls creates less resistance and the blower runs more efficient. Well it just depends on how fast you need to exchange the air. So if your blower is rated at 265 CFM, and it has no restrictions on the intake or exhaust side, it should take about a minute to replace all the air. Of course if the air your replacing it with is already hot, it doesn t do much too cool the grow room.