Best Fan Orientation for 2x3.5" HDD Bracket (Pictures and Temps)


What's an ITX?
Original poster
Dec 19, 2019

I am looking for some advice. My system is as follows:

Here are some pictures, to which I'll refer to :

The chassis fan is configured as intake and the CPU fan is configured also as intake, blowing towards the motherboard. I am a big "fan" of only adding additional cooling when it's needed. I'm in a situation where I definitely need it, and am looking for a recommendation on what to try next. My machine is located in the bottom of a cabinet (pictured) that has no door. It also doesn't have any venting in the rear.

So, I have tested a few different workloads. The first, is low CPU, low GPU and a steady workload to the two 3.5" drives. Here are my temperature measurements. I give the minimum temperature (the machine has been off for 1 hr, this represents starting state) and the maximum after 1 hour:

Sensor (HDD workload, no CPU or GPU workload)Minimum (system off for 1 hr prior)Maximum (1 hr test)
Mainboard31 C34 C
CPU32 C50 C
Chassis Fan365 rpm775 rpm
CPU Fan639 rpm1071 rpm
CPU Package32 C51 C
HGST 3.5" HDD33 C41 C
1TB nvme 33 C43 C
GPU Fan1496 rpm1504 rpm
Rear of Entertainment Cabinet23.2 C
Ambient (outside Entertainment Cabinet)19.8 C

I am happy with this configuration. I would like to keep my 3.5" drives at or below 40C.

The following data is with the same HDD workload, but adding Prime95 run at its default settings. Slightly higher ambient, but I'm happy with these CPU numbers, but have concerns about the 3.5" HDD numbers being at 44 C.

Sensor (HDD workload, Prime95 CPU workload, no GPU workload)Minimum (system off for 1 hr prior)Maximum (1 hr test)
Mainboard32 C48 C
CPU31 C86 C
Chassis Fan457 rpm1465 rpm
CPU Fan759 rpm1802 rpm
CPU Package31 C87 C
HGST 3.5" HDD38 C46 C
1TB nvme37 C44 C
GPU Fan1495 rpm1506 rpm
Rear of Entertainment Cabinet22.8 C
Ambient (outside Entertainment Cabinet)20.3 C

This data is with Heaven GPU workload, at max settings. I still have the HDD workload enabled. You can see that as the GPU heats up, we are significantly heating up the 3.5" HDD. Heat is getting trapped into this portion of the case, and the PSU fan being turned inward is dumping more heat here.

Sensor (HDD workload, Heaven GPU workload, no CPU workload)Minimum (system off for 1 hr prior)Maximum (1 hr test)
Mainboard29 C52 C
CPU34 C59 C
Chassis Fan410 rpm1027 rpm
CPU Fan667 rpm1445 rpm
CPU Package33 C62 C
HGST 3.5" HDD30 C53 C
1TB nvme33 C47 C
GPU Fan1494 rpm2322 rpm
Rear of Entertainment Cabinet27.9 C
Ambient (outside Entertainment Cabinet)20.4 C

Ok, the ultimate torture test. Yeah, this is too hot.

Sensor (HDD workload, Heaven GPU workload, Prime95 CPU)Minimum (system off for 1 hr prior)Maximum (1 hr test)
Mainboard23 C60 C
CPU34 C93 C
Chassis Fan262 rpm1475 rpm
CPU Fan438 rpm1816 rpm
CPU Package31 C95 C
HGST 3.5" HDD21 C57 C
1 TB nvme32 C50 C
GPU Fan1489 rpm2366 rpm
Rear of Entertainment Cabinet28.7 C
Ambient (outside Entertainment Cabinet)21.2 C

So, let's discuss!
  • I need to turn around my PSU. I haven't done this because I am not sure my custom cable will reach in the other orientation. I'll work on this next.
  • I don't have a lot of cooler options. The NH-U9S won't work with a intake fan on the side of the case and the NH-C14S won't work with the 2x3.5" mount.
  • I could consider a single intake fan on the bottom-front location, which might address the HDD temperatures.
  • I could also consider an exhaust fan on the rear, though in a closed cabinet I'm not sure this will help
What would you recommend?