Ventilation for a computer in a cupboard

As mentioned previously, this server will live life in a cupboard. If you know anything about computers you’ll know they like plenty of airflow and a very good way to break them, or at least dramatically shorten their life span, is to put them in an airtight cupboard. Alas this is what I wanted to do.

If you’re going to put your computer in a cupboard you obviously need to create some ventilation, or airflow, through the cupboard. The general rule of thumb when venting a cupboard is to use natural convection which is “cool air in at the bottom warm air out at the top”. However, this cupboard is in the main bedroom of the house and I didn’t want it looking like a computer cupboard with holes cut in the front of it, so I had to come up with a Plan B. The Plan B is shown below and whilst I’m the first to admit it doesn’t exactly look pretty inside the cupboard I’ll rarely open the doors so looks weren’t my number 1 priority.

Here you can see the cupboard in all it’s glory. So, cool air in top left, warm air out top right. Simple!

The fans on the front of the case suck the air in from the top left vent and the fans on the top and back of the case blow the warm air out of the top right vent.

The Antec case I’m using has a very large (22cm) cooling fan on the top of the case which sucks most of the hot air out of the case. The ducting I’d bought for this project was 10cm in diameter so I couldn’t just clip the ducting to the top of the case since most of the hot air from the case would blow into the cupboard instead of into the ducting. My solution was to build a “hood” out of batten and hardboard and, once again, whilst I doubt it’d win any awards for its looks it certainly does its job extremely well.

Initially, I connected the ducting directly to the vent grills at the top of the cupboard. However, what seemed to be happening was the “out” air was coming back into the cupboard and causing the air inside the cupboard to get warmer so I came up with the idea of attaching the ducting to those boxes. These too are made from batten and hardboard. I decided to put some 12cm fans in the boxes to create a nice through draft within the cupboard.

If you look closely at the picture you can see I’m also using some kind of circuit for the fans. This circuit is an mCubed T-Balancer MiniNG fan controller. It’s an excellent little thing and unlike the cheaper controllers on the market where you have to manually set the fan speed yourself, with this little beauty you get a couple of probes which you use to monitor the temperature of your chosen device(s), in this case the cupboard. The probes and circuit cause the fans to spin at varying speeds to maintain the chosen temperature. Very neat. I’m powering it using a 3.5″ IDE HDD Enclosure. The fans themselves are 12cm Noctua NF-S12 fans which are VERY quiet, even when running at full speed.

I’ve done a lot of experimenting with the fans (suck, blow, fast, slow) and I was surprised to discover that the cupboard remains nice and cool without the fans running at all. Fortunately they’ll be put to good use elsewhere, as will the fan controller.

The fan holes themselves are definitely required tho. I first tried the boxes before I’d cut the fan holes in them but the cupboard started heating up. I’m guessing this was either from the case and/or because the exhaust ducting is not air-tight and so warmer air, which should be blown out of the cupboard, was leaking back into it. Another possibility is that there is some heat transfer from the exhaust ducting to the air in the cupboard which caused the cupboard temperature to rise. Whatever the reason, the “fan holes” solve the problem.

All in all, I’m very pleased with the performance of the cupboard although at some point I may build a couple more “hoods”, one for the front of the computer case and one for the back of the case since it’ll improve airflow through the case. For now tho, it’s perfectly acceptable.

Left hand side of cupboard. The “in” side.

Right hand side of cupboard. This is the “out” side.

Note the smoke alarm screwed to the top of the cupboard in the last picture. This is an optical one which is specifically designed to detect slow-burning fires such as overheated wiring. The alarm is very much “belt and braces”. I’ve no doubt I’ve put together the computer properly and it isn’t a fire hazard, but better to be safe than sorry!