Scotty is correct. The usual problem with electrical rooms is getting the heat out of the room, and not injecting more heat. Having said that, having a small heater in the room, for those periods of extreme low ambient temperature and/or during plant down-times, is always a good idea. It doesn't take much heat to keep condensation off of electrical equipment.
I have just wrapped up several projects, where we had to do one (1) air change every 40s to suck the heat out of the room produced by several large drives (with xfmrs). Losses here are several hundred kilo-watts. The ambient temperature, at these locations, ranges from -45C to +35C, which is rather extreme. These rooms were also provided with several electrical unit-heaters for keeping the room from freezing during down-time (in winter months).
The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty.
Winston Churchill