All computers produce heat, but computer servers produce a lot of heat - so much that it usually costs a fortune to cool them down. So why is not this heat used, instead, to keep homes or offices warm? Actually, "nerd power" is already being tried out.
A sleek white box, which can easily hug a wal, looks nice enough as radiators go. But what is really exciting about it is what is going on inside.
Instead of hot water, it contains a computer connected to the internet, doing big sums and kicking out heat in the process. It was created by a Dutch start-up called Nerdalize, and could be part of a solution to a big problem for the tech industry.
Those clouds, that store "virtual" data, take the form of very large, noisy data centers containing tens of thousands of servers. To prevent the server stacks overheating, tech companies spend vast sums on cooling technology - more than a third of a data centre's hefty energy bill may go on air conditioning. With data centers estimated to account for 1.5 percent of global electricity consumption (in 2010), this wastage is costly to businesses and to the environment too.
Nerdalize's solution is, effectively, to spread their data centre across domestic homes linked by fiber-optic cable. The excess heat can then be used instead of going to waste.
The radiators take a little longer than average to heat up - about an hour, and a single unit would not be enough to heat a room in mid-winter. But, after a small set-up fee, the heat is completely free to users. Nerdalize gets its money for providing data services - its current clients include Leiden University Medical Centre, which uses the radiators to crunch through lengthy protein and gene analysis.
Size: 122cm x 70cm x 17cm - slightly fatter than a normal double radiator
Output: 1000W - about half the peak output of a conventional double radiator, but eRadiators can be left on all day
Cost: 400-500 euros (£290-360) to set up, then free of charge to use
Requirements: A fiber optic connection and an external wall
As Nerdalize started to look into the idea, they came across a paper published by Microsoft Research and the University of Virginia in 2011 on the potential for "data furnaces" to heat domestic and office properties. The energy savings were so significant, the paper said, that the IT industry could theoretically double in size without increasing its carbon footprint.
In fact, the initial impetus for that research was a slightly different problem. Microsoft was wondering what to do with all its old servers, which were less efficient and gave off more heat.
Nerdalize is one of a number of small companies to have taken these ideas forward, but Microsoft itself has so far put data furnaces on hold.
It, very well, might be a big thing but it does not look like it is going to be the big thing in the short term. Part of the reason is that the big tech companies are currently focused on making billions from the explosion in cloud computing, not saving millions by reselling the waste heat the sector produces.
There are also practical obstacles such as the cost of maintaining remote servers, and the issue of data security. Nerdalize's radiators are in a tamper-proof case, and use encrypted data but even so, there are probably a fair number of computing jobs that companies would not push out into people's homes.
Leaving that aside, it seems clear that data centers are not about to disappear. As more businesses move their storage to the cloud, their total number may decrease, but the number of very large centers is predicted to increase. The way in which these centers are cooled has become a central aspect of their design.
The memories, friends, likes and dislikes of all Europe are stored in a vast Facebook data centre in Lulea, Sweden, close to the Arctic Circle. Facebook is very proud of the green credentials of this 2013 plant, which is fed by renewable energy and employs "passive cooling". The idea is that instead of using air conditioning - "active cooling" - to keep servers cool, you locate the factory in a cold place, and design it so that the outside air can penetrate and circulate past the server stacks.
But one Swedish data services company argues that the Lulea plant is equivalent to leaving a heater on outside. "If you live in a cold climate, what do you do with heat? Do you ventilate it out in the winter?" asks Bahnhof's CEO Jon Karlung. "No, you do not. You use it to warm up houses."
Bahnhof's three data centers in central Stockholm do exactly that. Hot air circulates up through their buildings and is put through a heat exchanger, where it heats water pipes that connect up with a communal heating system. The company is one of a number of tech firms in the city that sell heat to a local energy company.
Bahnhof's data centres help to heat about 1,000 apartments and they have plans to build a new, larger data centre in the city, which could heat about 50,000. In a shift that no-one could have predicted five years ago, Karlung says their new centre will not be designed to stay cool, but to get as hot as possible.