I've also read that encoding videos in handbrake is another good way to raise the room temperature, it's technically 100% efficient because all of the energy given to the CPU, GPU, etc. goes into heat. The exception however, is the fans which also make noise as well as a little bit of heat. An Air Conditioner/Heat Pump will be more "efficient" because they operate by moving heat between two spaces, but you can't play games on an air conditioner (at least not supposed to https://www.youtube.com/watch?v=vPUl0Phg6mg)
I'm in QLD freezing my arse off, however, you could pair the computer with a thermoelectric generator to absorb the heat from the computer and power it. However, that probably won't work and would be an infinite power hack. It wouldn't make the room cooler but not make the room hotter.