I replaced the stock Corsair H100i fans with two Cooler Master JetFlo 95.0 CFM 120mm x 25mm High Performance Fans (pulling) plus added two Delta 151.85 CFM 120mm x 38mm Very Hi-Speed Server Fans (pushing) for push/pull configuration. I have these all drawing cool room air and pushing it through the radiator and into the case.
I replaced all stock case fans with Cooler Master JetFlo 95.0 CFM 120mm x 25mm High Performance Fans. I also added two Delta 151.85 CFM 120mm x 38mm Very Hi-Speed Server Fans (1 input on the top of the case and 1 exhaust on the back of the case) for great cooling when needed! The original 200mm case fan in the front of the case was left alone and remains in front of the case and I added one of the Cooler Master JetFlo fans to the front as well. Both are configured as input into the case. This configuration has proved very effective. With more input than exhaust it maintains a slight positive air pressure inside the case which prevents any seems or openings in the case itself from sucking any unwanted dust into the case.
(I took pictures as parts arrived. I pieced a couple together in a couple of the pictures the best I could match them up. These pictures are of the original build parts. Some parts have been upgraded now but not shown in the older pictures)
"Why so many fans?"
A few reasons why...
1) I live in Phoenix Arizona where it gets 100+ degrees Fahrenheit for 4 or 5 months of the year. The hottest part of the summer here gets to 120+ degrees Fahrenheit for about a month. Yes we have air conditioning. But to cool the house down and keep it at a comfortable 75 degrees Fahrenheit the power bill easily runs $700+ per month during those months. If I can run the AC a bit less and the fans a bit more the savings are very noticeable!
2) In the computer room I have this gaming computer, my server computer that runs 24/7 365 day per year, two 24" LCD monitors, a 42" LCD Television, full stereo system, a mini refrigerator and it's the western facing room of my house. So, it does get pretty warm, no hot, in this room at times during the summer months.
3) The Cosmos II case has spots for thirteen 120mm or 140mm fans depending on the configuration. The fans are inexpensive enough so why leave empty fan spots in the case? Cooler Master Jetflo fans are very high quality fans. 2000 RPM moves 95.0 CFM at 36.0 dbA With all fans at 100% it really isn't that loud. Hell, they actually help drown out my wifes bitching which is much louder than all these fans if you know what I mean! Doh! Just Kidding! They come with 2 silent mode adapters 1x 1600 RMP and 1x 1200 RPM for quieter operation if I choose to set them up that way. At $14 a piece they are very hard to beat.
4) The small $160 investment in these ten fans is a wise investment considering the harsher than normal circumstances this machine is under. I would DEFINANTLY rather have them and not need them than need them and not have them!
Right now I play BattleCrap 4 on all ultra settings. During full combat action I'm getting 100+ to 160+ FPS. With hours of non stop playing the cpu temperature stays around 40 C. (104 F.) with fans running at 50% RPM
One last thing, I plan to add 1 or 2, who knows, maybe even 3 more GeForce 1070 video cards someday down the road (bigger PSU too obviously) That's a lot of heat right there alone. Anyway, I am happy with it and it came in just over $3100 with plenty of headroom for overclocking in the future when needed.