I don't imagine it's that hard. Though not everyone has a server farm or mining...do they call it a farm too? Anyway...if they placed these in the basements of condos and apartment buildings where they also have access to solar or cheap renewable power, it could likely reduce their heating needs considerably. I suppose the main difficulty is that the power needs are substantial. Perhaps installing solar in a building might offset this. If it's a relatively small setup, maybe the increase wouldn't be that substantial.

Mining is already making some people in certain areas freak out, because much of the grid isn't built to handle the power usage. I personally blame the power company for this though, as the issues exposed by mining are proving that the grid isn't actually build to withstand the usage that the houses are rated for. Even without mining, more and more people are getting more and more devices, and not all of them will be the low power handheld variety. A group of a few nerds could easily put the grid under similar strain, even without mining. Mining just means that one nerd with a bit of cash will use as much power as a group of them. Or perhaps as much power as one nerd that's into AI or video/graphics rendering or some such.