My Raspberry Pi 4, running without a case, has an idle temperature of 54°C. With the official Pi 4 case the idle temperature jumps to 72°C.
The official case is completely hotboxed, allowing for absolutely no airflow. Since the Pi 4 begins to throttle the CPU at 80°C, this makes the official case a design disaster and useless without the addition of active cooling.
The noctua range of fans get great reviews and are super well made – but you pay a premium for quality; they're pricey compared to other brands. I picked the 40mm x 20mm NF-A4x20 5v for mounting on the outside of the Pi case.
If you wanted a slimmer fan to mount inside the case, go for the 40mm x 10mm NF-A4x10 5v.
Case Modding
I cut a 38mm hole in the top part of the case with a hole saw, at the end of the case away from where the Pi's USB and Ethernet ports are. Placing the fan over the hole, I marked out and drilled some screw holes for the screws provided with the fan.
In the side of the Pi case base, I've drilled 6, 2mm holes at 1cm intervals as an air inlet/exhaust.
Fan Connector Modding
The fan comes with a big fat 3 pin connector, too big to fit on the Pi's GPIO pins. The fan does come with a 2 pin adapter which you can add your own connectors to, but I chose not to use it as it would just take up space in the Pi case. Instead, I cut off the original connector, removed some of the wire insulation and crimped some new DuPont connectors.
The black wire connects to one of the Pi's ground pins. The red wire connects to one of the Pi's 5v pins. The yellow wire is not required - I crimped a connector anyway, but then just keep it out of the way with some tape.
Suck vs Blow
Should you mount the fan to blow cooler air on to the Pi board and vent the warmer air through the side holes, or use the side holes as an inlet for cooler air and suck the warmer air away from the Pi board?
The only way to really know is to mount the fan both ways, stress test the Pi, measure the temperature and compare the results. Install the stress package on the Pi using apt with command:
sudo apt-get install stress
For the tests below I have used the stress command with the cpu, io, vm and hdd parameters, with 4 workers for each, running for 5 minutes (300 seconds):
stress -c 4 -i 4 -m 4 -d 4 -t 300
The Pi's temperature can be measured with:
vcgencmd measure_temp
For the tests below, I sample the temperature every 5 seconds in a loop for 7 minutes (84 iterations) to record temperature rise and drop off:
for i in {1..84}; do printf "`date "+%T"`\t`vcgencmd measure_temp | sed "s/[^0-9.]//g"`\n"; sleep 5; done
Test 1 – Blow
Mounting the fan with the sticker side down to blow air onto the board, connecting the power pins, closing the case and running the stress test gave the following results:
$ stress -c 4 -i 4 -m 4 -d 4 -t 300 stress: info: [1074] dispatching hogs: 4 cpu, 4 io, 4 vm, 4 hdd stress: info: [1074] successful run completed in 303s
$ for i in {1..84}; do printf "`date "+%T"`\t`vcgencmd measure_temp | sed "s/[^0-9.]//g"`\n"; sleep 5; done
10:59:42 38.0
10:59:47 37.0
10:59:52 43.0
10:59:57 45.0
11:00:02 47.0
11:00:07 48.0
11:00:12 48.0
11:00:17 49.0
11:00:22 49.0
11:00:27 50.0
11:00:32 50.0
11:00:37 51.0
11:00:42 51.0
11:00:48 52.0
11:00:53 52.0
11:00:58 51.0
11:01:03 53.0
11:01:08 52.0
11:01:13 52.0
11:01:18 53.0
11:01:23 53.0
11:01:28 53.0
11:01:34 53.0
11:01:42 52.0
11:01:48 53.0
11:01:55 52.0
11:02:00 54.0
11:02:05 54.0
11:02:10 54.0
11:02:15 53.0
11:02:20 53.0
11:02:25 53.0
11:02:30 53.0
11:02:35 54.0
11:02:41 54.0
11:02:46 54.0
11:02:51 53.0
11:02:56 52.0
11:03:01 54.0
11:03:06 53.0
11:03:11 54.0
11:03:16 53.0
11:03:21 54.0
11:03:26 54.0
11:03:31 54.0
11:03:36 54.0
11:03:41 54.0
11:03:46 54.0
11:03:51 54.0
11:03:56 54.0
11:04:01 53.0
11:04:06 54.0
11:04:11 53.0
11:04:16 54.0
11:04:21 53.0
11:04:26 54.0
11:04:31 53.0
11:04:37 54.0
11:04:42 53.0
11:04:47 54.0
11:04:52 49.0
11:04:57 46.0
11:05:02 45.0
11:05:07 44.0
11:05:12 46.0
11:05:17 43.0
11:05:22 42.0
11:05:27 42.0
11:05:32 41.0
11:05:37 40.0
11:05:42 41.0
11:05:47 40.0
11:05:52 40.0
11:05:57 41.0
11:06:02 39.0
11:06:07 40.0
11:06:12 39.0
11:06:17 39.0
11:06:22 38.0
11:06:27 38.0
11:06:32 38.0
11:06:37 38.0
11:06:42 39.0
11:06:47 38.0
Test 2 – Suck
Re-mounting the fan with the sticker side up to suck air away from the board, connecting the power pins, closing the case and running the stress test gave the following results:
$ stress -c 4 -i 4 -m 4 -d 4 -t 300 stress: info: [1041] dispatching hogs: 4 cpu, 4 io, 4 vm, 4 hdd stress: info: [1041] successful run completed in 302s
$ for i in {1..84}; do printf "`date "+%T"`\t`vcgencmd measure_temp | sed "s/[^0-9.]//g"`\n"; sleep 5; done
11:22:41 39.0
11:22:46 40.0
11:22:51 46.0
11:22:56 49.0
11:23:01 50.0
11:23:06 51.0
11:23:11 52.0
11:23:16 52.0
11:23:21 52.0
11:23:26 52.0
11:23:31 53.0
11:23:36 54.0
11:23:41 54.0
11:23:46 54.0
11:23:51 55.0
11:23:56 55.0
11:24:01 55.0
11:24:06 54.0
11:24:11 55.0
11:24:16 55.0
11:24:22 55.0
11:24:27 54.0
11:24:37 55.0
11:24:42 56.0
11:24:47 57.0
11:24:52 56.0
11:24:57 57.0
11:25:02 55.0
11:25:07 56.0
11:25:12 56.0
11:25:17 57.0
11:25:22 56.0
11:25:27 57.0
11:25:32 56.0
11:25:37 57.0
11:25:42 58.0
11:25:47 58.0
11:25:53 58.0
11:25:58 58.0
11:26:03 57.0
11:26:08 58.0
11:26:13 57.0
11:26:18 58.0
11:26:23 58.0
11:26:28 57.0
11:26:33 58.0
11:26:38 57.0
11:26:43 57.0
11:26:48 58.0
11:26:53 58.0
11:26:58 59.0
11:27:03 58.0
11:27:08 58.0
11:27:13 57.0
11:27:18 58.0
11:27:23 59.0
11:27:28 58.0
11:27:33 58.0
11:27:38 58.0
11:27:43 58.0
11:27:48 55.0
11:27:53 51.0
11:27:58 49.0
11:28:03 48.0
11:28:09 47.0
11:28:14 46.0
11:28:19 46.0
11:28:24 46.0
11:28:29 45.0
11:28:34 45.0
11:28:39 44.0
11:28:44 44.0
11:28:49 43.0
11:28:54 44.0
11:28:59 44.0
11:29:04 42.0
11:29:09 42.0
11:29:14 42.0
11:29:19 42.0
11:29:24 43.0
11:29:29 43.0
11:29:34 42.0
11:29:39 42.0
11:29:44 42.0
Comparison
Blowing air keeps the Pi cooler than sucking air, with temperature ranges of 37°C-54°C and 39°C-59°C respectively for this fan/vent combination.
When sucking air, the Pi doesn't reach the original idle temperature 2 minutes after the stress test has ended.
Parts list and prices
| Part | Price | Link |
|---|---|---|
| 38mm Hole Saw | £4.59 | https://www.ebay.co.uk/itm/143196534863 |
| DuPont Connectors | £2.60 | https://www.ebay.co.uk/itm/264250195674 |
| Noctua NF-A4x20 5V | £13.40 | https://www.amazon.co.uk/gp/product/B071W6JZV8 |
