I agree with Philip on this.... I have 33 rigs in my warehouse, and I am desperate to keep the temps down.
Those box fans will be a futile attempt.... you need a more powerful strategy to move the hot air out.
I have bought 2 of these to fix my temps and still I am not satisfied with the current temps 36-37c
I have to resort to mining XMR to reduce watts and temps.... but I am longing to go back to ETH and ZEC at full speed!
It really depends on your layout. For my shed, it's very narrow so I don't think I will have a problem as it will pull hot air out very fast since everything is closer. I also left expansion spaces just in case. If I have to guess based on the pulling power I'm feeling, these box fans are probably 1500 CFM or higher so x 5 = 7500 CFM. They feel very weak when only 1 or two is on but when all 5 is on, the negative pressure is so strong it will slam the shed doors together. Houston weather is very weird in that it can be very hot during the day but chilling at night so the thermostat control reduce my operating cost as few of the fans are not running right now.
If you can remove the heat faster than it can build up, you can keep unlimited number of rigs. The issues most of us have is that we let the hot air recirculate back into the intake side as well as the room. This is why I had to go to the server RACK design on top of using my portable heat wall to contain the hot zone and making the total CFM in that area smaller so I can use cheaper and lower CFM fans ( 2 x 4600 CFM). They are good looking as they have grills that looks like normal AC vents and are very quiet while consuming very little wattage. My current setup right now only use these 2 exhaust fans blowing hot air into the attic, I don't even use intake fans, the negative pressure does the work for me.
Today is 85F, very hot day in TX for Feb! I'm currently running over 45 rigs in the garage with 15 more rigs to be installed. No temp issues. Before this design, I was barely able to run 20 plus rigs and had to use a ton of box fans unnecessarily just recirculating that hot air! For the new design, I wanted to keep my design minimalist and as cheap to run as possible. I also try to keep it clutter free and as sexy as possible too. =)
@kobazik - I use the Platinum 1200 W to power 7 GPUs not 6. You should have no issues, they are beasts. Don't bother with EVGA 1600 as they do require 240V, if you have that, then no issues but they're also much larger so it's very tight fit for the Rosewill. EVGA 1200 / 1300 are better when on sale. Save the money and buy more GPUs especially if you have no plans for more than 6GPU rigs. Wait until you see my server PSU review / setup for the Shed, it will make you continue thinking of alternatives. =)