Hello there Bruiser. I myself am a closet grower and just like you I struggled with overheating and ventilation problems when I first began growing in a smaller space. I know some of the other guys have given you some pointers and I would like to suggest this to you. I myself use an item called an Squirrel Cage Blower which is highly effective at removing heat. These blowers are basically like high powered bathroom exhaust fans. I have done my best to calculate the cubic feet of your room with the information you provided. It is 460 Cubic Square Feet large. I suggest you go to this website http://www.mdhydro.com/squirrel-cage-fans.html and consider buying the 465cfm model(CFM=Cubic Feet Per Minute). They are very easy to setup and the website I directed you too is very affordable and very possibly the cheapest place on the net. I buy almost all my equipment from these guys and I trust them 100 percent. I'm almost positive that this will eiminate your heat problems. Now I'm not sure if you know about rates of air exchange but it is advised that you cycle all the air out of your room at least once per minute or five time a minute for optimum results. If you don't know how to calculate that what you do is take the cubic square feet of your room and purchase a cage fan that meets your CSF(cubic square feet) or exceeds it. With your 460 CSF grow area you would need the 465cfm model to exchange air once per minute with five cfm's left over. In order to exchange the air in your room five times a minute you will need a exhaust fan capable of 2300cfm's a minute which is damn near impossible to find so I would suggest going with their 800cfm model if you want to push more air out of the room faster. I hope I could help and good luck to you.