[zrm]

~35 watts isn't actually all that much heat load, and that's what you get from the likes of a business-class Core i5 at the loads routing packets would put on it (i.e. basically idle). Something like Atom or AMD Bobcat is <15 watts.

Another thing to keep in mind if you're worried about power/heat is that 3.5" spinning rust can pull >5 watts per spindle. I've seen 15K drives pull close to 20. But an SSD is close to nothing and so are most 2.5" laptop spindles.

[generalpass]

I'll concede that a small closet can get pretty warm from even lower power devices. However, as long as the CPU isn't overheating and the space is clean and dry, it doesn't matter.