A common fault of satellite receivers is that they overheat because you've installed them in a warm room or in a place that doesn't permit cooling. Electronic equipment should be placed on a cool open shelf and not "stacked" on other warm equipment.
One way to improve cooling without using a fan is to locate the position of the hottest part of the Digibox cabinet (usually the power supply area) and to stand the Digibox on its end or side so that the hottest part is at the top. Make sure there are air vents near the top and the bottom.
Now natural convection will drag cool air in through the bottom vents and will pull it upwards, forcing hot air out of the top. This may not look very elegant but stacking your equipment in this way can make it last MUCH longer!
Will the standard Digibox run cooler in standby?
No. The only difference between standby and "on" is that the audio and video outputs are disabled. Everything else is working. This is intentional so that Sky can send a signal via satellite to tell your Digibox to "phone home" or to update its software or its viewing card.
A Digibox with a Hard Disc Drive may run cooler in standby, provided the HDD is not spinning.
The single item that produces the most heat is often the CPU (microprocessor). Some companies advocate the fitting of just a heatsink without a fan. Here's why that may not help very much:
A heatsink is like a bucket. Basically, it soaks up heat from the CPU until the "bucket is full". If it can't get rid of that heat then it can't soak up any more and the CPU gets hotter and hotter.
The only ways the heatsink can get rid of its heat are:
1. by direct radiation to the metal cabinet. The cabinet gets hotter and radiates the heat away to its surroundings. The external air also takes heat away from the cabinet. This doesn't work too well with a plastic cabinet!
2. by airflow. Natural airflow is upwards, which means you need an air inlet at the bottom and an air outlet at the top (see our first suggestion, above). Hot air can't travel sideways unless there's something to push it (a draught from a window or door, or from a fan).
So in the long term (several hours) a heatsink without a fan in a fully enclosed cabinet is bound to be far worse than one with a fan that pushes cooler air past it. It's impossible for it to be otherwise, just as it's impossible for a bucket to hold more water until some is emptied out.
This is not easy to grasp, and I expect arguments from the mentally challenged, but it's true. It's not difficult to prove it by taking measurements inside a PC case over a number of days. (Don't try this at home, kids. If you disconnect the fan in a PC the CPU won't last long!)
Think of it another way. You have a hot water radiator (the "heatsink) in your living room and the heating pump (the "CPU") is permanently on, pumping hot water into it. The windows are open a fraction. The room gets hotter and hotter until an equilibrium is reached, whereby the slight cooling effect of the open windows and the heat escaping through walls, ceiling and window glass exactly matches the heat coming from the radiator.
Now imagine the radiator (=heatsink) is four times as large. Is the room going to get hotter or cooler.
Well it's likely to get hotter because the radiator is now more efficient at radiating heat into the room (=receiver).
But, in the case of a satellite receiver this is bad news. The central heating pump (the CPU) is also in "the room" so it's going to get hotter, too!
In these circumstances, the only cure is to open the windows wider and or fit a fan to suck the hot air out of the room.
So, the point I'm making is that a bigger heatsink isn't necessarily much help if it's simply radiating heat into the cabinet where the CPU is. You really need a better airflow to get the heat out.