I know this has already been marked as a correct answer, but it really needs some serious clarification, as I see this kind of stuff being drawn up off data-sheets all the time:
Cooling calculations for switches should only be *very* loosely tied to BTU output of the power supply, with special attention to PoE scenarios. Keep in mind a few things:
- Your 250/640/1025W power supply almost certainly won't be dissipating 250/640/1025w of heat at the switch, unless at absolute-max load, at environmental limits, and all PoE devices are in the same room.
In a PoE scenario, a significant amount of this power is being distributed to PoE devices, and this heat is dissipated at the remote location *Not at the switch* (The PoE device will dissipate head where the PoE device is, or in cabling between the switch and the PoE device)
A good way to do calculations for this stuff, is to actually measure power consumption from a few switches at expected load, and work out PoE draw. Taking numbers from data-sheets can lead to ludicrous over-estimation of cooling (& UPS power/generator) requirements. I have seen communications rooms with 10-fold more cooling (& UPS) capacity than required, purely because they worked off power supply stats rather than actual application & load values...
To give you an idea, a 3750-48PS has a 540W power supply, but with 24 ethernet ports connected and no PoE it's only drawing 70W - That is nearly a 1000% over-estimation in power consumption if you go purely off your PSU statistics. It gets even more misleading (for local cooling, but not UPS) if you hook up PoE gear, as your power consumption goes up, but the power/heat is transported out of the room to a remote device!
Spend some time doing the cooling calculations, with real world loads! It's not going to break your connectivity, it's just going to be expensive! :)
