The NH-D9DX i4 includes an extra set of fan mounting clips for users who want to achieve even better cooling performance by adding a second, optional NF-A9 to the front fin stack. Using the y-cable supplied with the NF-A9 PWM retail fan, both fans can be connected to one CPU fan header.**
**The optional front fan will sit above the RAM and depending on the height of the RAM modules, the fan may have to be moved up so far that the total height of the cooler exceeds 110mm. As a result, the cooler may no longer fit some 3U cases. In order to guarantee full 3U compatibility in dual fan mode, please use low profile memory with up to 22mm height.