The thermodynamics of negative entropy: bounds on heat generated by computers (opens in new tab)

Yes, it's essentially "free" - an electrical heater does the same thing as a computer in this regard. My MacPro3,1 (lovingly called The Behemoth) produces enough heat to make my home office comfortable through most of the winter. The electrical bill is astronomical, however. And it really sucks in summer.

I always wondered why data centers aren't exporting heat to the local community the same way many power plants do - it's a lost opportunity. It would also be a great secondary heat source for many skyscrapers if they designed them with a well-placed datacenter inside.

> Under those conditions, is my computer use essentially free?

It's 'free' when compared to an electric heater, but not when compared to a heat pump (e.g. a food refrigerator). Heat pumps can use their energy input to divert heat from a cool reservoir, in addition to simply creating additional heat.

So if you want to generate heat even more efficiently, keep a fridge in your room and fill it with water or soft drinks (water has a high thermal capacity).