The topic of energy required to run all digital infrastructure continues to be an important one. Following on from the earlier Digital Infra Network presentation on the future of energy, the link between energy and information is at the heart of a concept called combined heat and computation. Energy consumption and heat generation is an inevitable consequence of the need for more data processing. Therefore, rejecting the heat into the environment without recovery to displace other energy intensive processes that require heat is now regarded as unsustainable. But heat reuse from data centres has challenges as demonstrated via analysis of the RISE testbeds.