A recording studio design consultant in Hollywood once pointed out an interesting point to me, in regard to racked outboard audio equipment.

He explained to me: “people think that heat rises, but heat doesn’t rise, hot air rises, but that's different. Usually with electrical devices heat is localised, therefore its best, as with heat sinks  or fans etc. to have a localised solution. Especially with racked devices, particularly with tube equipment.”

I felt at the time and still do, that was a perspicuously important insight.

Now it is a well understood phenomenon with electrical devices generally, that both excessive heat and switching devices on and off, constantly heating and cooling internal materials, are common causes of component failure. 

This is indeed common to all devices, regardless of brand, model or cost.

Therefore, all my RME and ancillary units are given one full unit space beneath and above, in addition to the sides where the units have air cooling slits, to ensure adequate dissipation of heat in a globally efficient manner.

They are deliberately not enclosed, as in a walled in rack, but used in a large but entirely open rack, with copious amounts of free air, all around. I have not found it necessary to introduce additional fans or provide other cooling methods whatever, finding the current solution as described, entirely satisfactory. 

Heat simply doesn’t appear to be a problem at all, such that I don’t think about at all these days.

However, when I first contemplated purchasing the three RME units in the rack.

I devised this plan to avoid any undesirable heat issues.

Thank The Lord. It worked!