Fun fact, but CPUs/GPUs/etc are almost 100% efficient at converting electricity to heat, as they don't give off light energy like a heater would, via its glowing coils.

So, theoretically, heating your house with CPUs would be greener than using central heating...

If you live in a cold area, a home server's heat wouldn't be wasted, in fact it would theoretically lower your heating bill(by .01% or less, but hey!) as less electricity would be used on the less efficient heater.