Introduction: Computer Cooling Box


CrashPlan is cutting off their home user backup subscription plan. I originally chose CrashPlan** for home use because it supports both network drives AND Linux computers. While not as well polished or as easy to use to BackBlaze**, it did save my butt when my local NAS failed last year.

**I don't want to sound like an advertisement, but if your needs are limited to a Windows PC or laptop, you cannot beat BackBlaze in ease-of-use. I've had to restore my laptop several times over the years and BB has always come through for me.

With CrashPlan going away, and BackBlaze not offering support for Linux or network drives, I decided that it was time to "roll my own" solution. The idea is pretty straigh forward, take a rarely used "extra" PC, attach some storage to it, set up rsync services, and then place the machine a safe distance from the house ("offsite" backup in case of fire or flood).

The tool shed seemed the ideal location, locked and as far from the house as possible within my property. Unfortunately, the environment there can be quite hostile towards a PC with natural and wood dust constantly a problem.

I needed a box, that I could place the computer and storage drive in, that would keep the machine breathing reasonably clean air.

Step 1: Gather Materials

In addition to a computer(1) with adequate storage, you will need:

  • The actual box to put everything inside of.
    • You can build a box, re-use and existing box, or buy a box.
    • A clear, hanging file, box from Wal-Mart was large enough to serve my needs and cheap.
  • A HEPA filter
    • There are a lot of air filtration devices on the market, most of which have replaceable HEPA filters. The filters themselves can cost between $10, and go as high $60 or more.
    • I trick that I found was the vacuum filters are also often HEPA rates, better sized for project work, and a lot less expensive.
  • A temperature controller/relay
    • My original plan was build what I need using an Arduino Uno, but a dedicated 12v device was cheap enough on Amazon
    • I used the 12v DROK 1. The fact that it was designed from 12v in/out was a nice bonus since the computer fans that I had on hand were also 12v.
  • A fan, or fans, to move the air
    • I used to two 12v PC power supply fans, scavenged from computers long dead.
    • You can also buy similar fans on Amazon for less than $10 each.
  • A power supply
    • Another scavenged part. I tend to keep every power supply that I come across, even after the original device is long gone. In this case, I happen to have a 12v 3a supply fit the bill perfectly.
    • You could reuse an old USB drive power supply, or even an old laptop power supply.
    • Or, just buy from Amazon.
  • Misc.
    • Screws to mount the fan(s)
    • Electrical tape for wiring (and solder and a solder gun)
    • Duct, or similar, tape to seal gaps and tape down loose wires
    • Possibly some extra wire to run between the fan(s) and the temperature controller, depending on your configuration

Step 2: Build the Box

Building the box basically consists of these steps:

  1. Arranging the PC and storage inside the box - determine the best layout for your hardware.
  2. Based on the above, select where the air inlet should be (where you will place the filter) and where the outlet will be (where you place the fan(s)).
  3. Determine the best location and mounting for the temperature control to ensure that the sensor is placed in a good location to detect the heat, and not get smashed.
  4. Cut the hole for the inlet (filter):
    • Use the filter to draw an outline of the "as cut" size. If you are using a plastic box, like I did, you can use a retractable utility knife to score the plastic to cut the opening (see TIP below).
    • Test fit the filter and trim as needed to ensure a nice, but snug, fit.
  5. Cut the outlet:
    • Rather than try to score a round hole in the plastic, I used my hole saw and drill to cut a hole as close to the fan size as possible. The plastic is surprisingly tough, so take your time and let the saw do it's job. Rushing it will only result in cracks.
    • Drill four small holes to attach the fan(s) to the box.
      • The fans will already have holes for mounting. Simply make a paper template to transfer the location to the box, with a sharpy, and select a drill bit that matches the hole size on the fan.
    • Drill a fifth hole to pass the fan wires through to the inside of the box. Usually, you can use the same drill but as above.
      • Note that the fan will probably have a wire routing notch pre-cut. Align your fifth hole with that notch for a clean appearance and fit.
  6. Mount the fan(s), passing the wires through the fifth hole and into the box.
  7. Mount the temperature controller and connect the controller's output to the fan(s) wiring.
    • I did NOT solder these connections. You can use a wire nut, or just "twist and tape" like I did. The reason for NOT soldering these is pretty simple: I want to be able to easily replace the fan(s) if/when the bearings fail.
  8. Connect the power supply output (12v DC) to the temperature controller input
    • I drilled a hole in the box to feed the output side of the power supply into the box and soldered the connection between the power supply and controller.
  9. Tape any exposed wires with electrical tape.
  10. Secure any loose wires with duct tape. I just taped them to the inside of the box.


  • Score, do not cut, the plastic. I found out the hard way that the plastic can be brittle and tends to crack instead of cut. To avoid the cracking problem, repeatedly score the plastic along the cut line. It doesn't take any longer to do, and will result in a crack free hole.

Step 3: Temperature Sensor and Wiring

I set the temperature sensor to turn on the cooling fans at 30C. You could probably go higher, maybe all the way to 40C, but I wanted to make sure that the box didn't overheat in the summer.

The controller itself is placed inside the small compartment built into the hinged top. I drilled a hole to pass the wiring and sensor down to the main box below. I used duct tape, liberally, to ensure that there were no air leaks and taped the sensor where it would be aware from the PC fan or the box fans.

Step 4: Assemble and Deploy

With the controller, sensor, filter, fans, etc. all in place, all that is left to do is to put the PC and USB HDD into the box and close it all up.

I mounted the box out in my tool shed, away from the house, and connected it to my network using Ethernet over powerline adapters. It's been in place for 6+ months and has been working great. We're just now getting into the hot months in Michigan, so I will keep an eye it to see how it continues to perform.

One nice thing is that the PC in the box is running Webmin, so I can remote check the PC status, including temperature.