Answered this question yesterday ....
Short answer .... it's not a good idea from a cost standpoint
Switching from 2700 rpm fans to 1500 rpm fans will reduce your cooling capacity by almost 50% ... adding the 2nd set of fans will give you back 20%. So your cooler investment is now $112 for the (4) Nocs plus $100 for the cooler or $212..... now add in the splitter cables or Fan PCB and you at $232 .... and your performance will be about as good as a Hyper 212.
Alternate 1 - Buy better fans which also happen to be cheaper. These are half price and the Phanteks outperform the Nocs as shown here:
1. Phanteks takes the Nocs by 3C at 300 lower rpm
http://www.overclockersclub.com/reviews/phenteks_f140/3...
2. Phanteks takes the Nocs again .... see chart at bottom.
http://www.silentpcreview.com/article1345-page7.html
DV version -
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
PWM Version -
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Option a) You can use the Phanteks Fan PCB to put all 4 fans together. Connect the PWM signal from the H100i to hub and then connect the hub to all 4 fans......
THEY MUST BE 3 pin DC fans. This will save you money on the fans, and eliminate the PWM fan hum / clicking that ya get when ya run PWM fans at low speed.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Option b) You can use the Swiftech Fan PCB to put all 4 fans together. Connect the PWM signal from the H100i to hub and then connect the hub to all 4 fans......
THEY MUST BE 4 pin PWM fans. This will [EDIT remove "save"] cost you more for the fans, and possibly subject you to the PWM fan hum / clicking that ya get when ya run PWM fans at low speed.
http://www.frozencpu.com/products/20988/ele-1196/Swifte...
NOTE: There's a known issue with Corsair's PWM implementation. If you gang multiple Corsair Fans together you lose the ability to provide speed control....see this post by Darla
http://www.overclock.net/t/1506812/the-best-pwm-rad-fan...
Both options have a cable to the PSU to provide power so the load from multiple fans is not an issue. Both report the correct speed of the fans tot he MoBo or fan controller. However, for the above reasons stated by Darla, I would STRONGLY recommend option a) using the cheaper non-PWM fans. I have 3 of those Fan PCBs and they work just mahvelous:
6 x Phanteks SP-140 on 420 radiator => PCB No. 1 => MoBo Header CHA_1
4 x Phanteks SP-140 on 280 radiator => PCB No. 2 => MoBo Header CHA_2
5 x Phanteks SP-140 case Fans => PCB No. 3 => MoBo Header CHA_3
I used FanXpert to Auto-Setup the fan Curves, tweaked them a little and haven't touched them since. CPU temps top out at 72C under stress testing at 46 multiplier / 46 cache / 2400 and GFX card temps don't break 44C ...and you can't tell if the computer is on using your ears.
If it were me, I'd take that $112 fan budget and 420 splitters budget ($132) and buy a Swiftech H220-X for just $8 more or the H240-X for just $18 more and sell the H100i .... be far more cost effective ... you will have a better product, better performance and a lot more money in ya pocket.