Rotterdam (The Netherlands), has already been using a similar method of providing heating to a huge portion of the city since 2006. 'Stadsverwarming' (directly translated to city-heating), uses excess heat that's produced in the city's port/harbour to provide heating to houses and businesses all over the city.

(It's also the largest port in the world outside of Asia)

There are other parts of The Netherlands which already use the excess heat from large scale data centers for exactly the same thing. Cities such as Amsterdam, Eindhoven and Groningen for example.