a single 600mm2 exhaust fan which i think is about 70cmm or 2000cfm

i have to guess because it is a second hand with no label what so ever   and it is doing the job just fine, also when it get's very hot and i have to increase the fans rpm( of the miners) i simply open the door of the hot room to allow some of the hot air to go outside, the intake for the cold room is on the opposite side so the hot air has noway of going back.

i know many people say that you need at least 150-200 cfm for each miner which means i will need about 200*40 =8000 cfm but really for this set up a single fan is doing the job, in fact it stopped working once so i had to rely on only the pressure of the miners' fans to push the hot air out of the door and temps were not even that high, i think as long as the hot room is large enough then there is plenty of room for the hot air to find it's way out. i know this might not make sense if you would go by the BOOK , but it's working for me



I will take more pictures when i set up the coming miners to give  you a better overall view.