> excess heat to be used for residential building heating

In the late 90s I worked at an insurance company in leafy Surrey[1]. I was told that they used to use their IBM mainframe to heat the swimming pool[2] effectively for free; when they upgraded they had to buy and run a heating system for the pool as the new mainframe didn't pump out enough heat.

[1] In England, south west suburbs of London to be precise.

[2] yes it had an indoor pool, badminton courts, outdoor tennis courts and other facilities - a great place to work.