Image copyright ALAMY

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 isn't this heat used instead to keep homes or offices warm? Actually, "nerd power" is already being tried out.

Ask Jerry van Waardhuizen about his new radiator and you get an excited response. "I'm very enthusiastic," he says. "It's a beautiful thing." The sleek white box, which has been hugging his wall for two weeks, looks nice enough as radiators go. But what's really got Waardhuizen excited is what's 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.

We talk about data being "virtual" and stored on a "cloud". In fact, those clouds take the form of very large, noisy data centres 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 centres estimated to account for 1.5% of global electricity consumption (in 2010), this wastage is costly to businesses and to the environment too.

Image copyright Jerry van Waardhuizen Image caption Jerry van Waardhuizen is very excited about his new radiator

Nerdalize's solution is, effectively, to spread their data centre across domestic homes linked by fibre-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, Waardhuizen says - and a single unit won't 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. During this year-long pilot, its clients include Leiden University Medical Centre, which uses the radiators to crunch through lengthy protein and gene analysis.

If you live in a cold climate, what do you do with heat? Do you ventilate it out in the winter? Jon Karlung, Bahnhof CEO

The server in the radiator does not stop working when the unit is turned off, but the heat is pushed into an extractor on the outside wall. And in the unlikely event that a user needs heat but the internet is down and the radiator has nothing to work on, it starts performing dummy equations.

Nerdalize have what any start-up needs, after a good idea and financial backing - a nice story. In 2012, Mathijs de Meijer and Boaz Leupe were renovating a run-down house when they accidentally broke the thermostat. "Mathijs was working on his laptop and after a while of really trying everything to stay warm, he said: 'Well, you know what, how about we take 100 laptops, put them into one of the rooms and then we'll have nerd-heat heating our house?'" says Florian Schneider, who co-founded the company with the erstwhile housemates. "And that was more of a joke - and then very quickly turned into, 'Wait, maybe this is not such a stupid idea after all.'"

As they 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.

The Nerdalize eRadiator

Image copyright Other

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 fibre optic connection and an external wall

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. The authors noted that the technology required to remotely control and reboot servers had arrived just in time to play a role in cloud computing and "big data". They envisaged apartment blocks heated by data centres in the basement, and remote "micro-data centres" placed in people's living rooms.

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.

"After we worked on the project together, I spent about seven months working with Microsoft to try and figure out, you know, 'Is this going to be the next big thing?'" says Kamin Whitehouse at the University of Virginia, one of the authors of the paper. "And it very well might be a big thing but it doesn't look like it's going to be the big thing in the short term."

Part of the reason, Whitehouse says, 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.

Bahnhof's new data centre will not be designed to stay cool, but to get as hot as possible

In addition, there are some limitations. "A network of data furnaces is not equivalent to a data centre," Whitehouse says. While Nerdalize's radiators are ideally suited to labour-intensive tasks on a small dataset, like gene-mapping or video game rendering, other jobs require fast processing of large amounts of data.

This is best done by multiple servers working in parallel on different parts of a dataset and talking to one another. Do a web search and a million different computers look at a million parts of the web before the results are collated in the blink of an LED light. The Netherlands boasts a comprehensive fibre-optic network, but the fastest way for computers to work together is still to put them in the same room.

There are also practical obstacles, Whitehouse says, such as the cost of maintaining remote servers, and the issue of data security. He notes that 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. They would want to have them in a secure data centre. So again that limits the total market share they could achieve."

Florian Schneider disagrees. He says Nerdalize's dispersed network of servers is more secure than a data centre, which represents a single point of failure. "It becomes nearly impossible to know what data is where, when it is there and how to get to it," he explains.

Find out more

Florian Schneider spoke to Click on the BBC World Service

Listen to the interview on iPlayer or get the Click podcast

Leaving that aside, it seems clear that data centres 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 centres is predicted to increase. The way in which these centres 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.

Image copyright Getty Images Image caption A server room in Facebook's plant near Lulea (Getty Images)

Image copyright Getty Images Image caption The "relief room" at the Facebook plant (Getty Images)

Greenpeace has praised Facebook for its "important leadership role" in defining best practice for energy efficiency in the data services sector. Not only has the company committed to becoming 100% powered by renewable energy, it has shown willingness to share knowledge about green design through an initiative called the Open Compute Project. 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 don't. You use it to warm up houses."

Bahnhof's three data centres 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 municipal 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.

Karlung believes Facebook's 100-megawatt Arctic Circle plant might have provided heat to almost 200,000 homes, but since Lulea only has a population of about 50,000, the opportunity has been lost. If Facebook had built their centre close to a city, they would have paid more for the land, but Karlung says that would have been more than compensated for by energy sales. "Nobody had the idea," he says, adding mischievously: "Every time you log into Facebook, you kill a polar bear." (Karlung was the custodian of the Wikileaks servers throughout 2010, and he has not lost his fondness for controversy.)

Image copyright Bahnhof Image caption Pionen, Bahnhof's James Bond-inspired data centre in Stockholm

Image copyright Bahnhof Image caption The waste heat from one of Bahnhof's data centres meeting the municipal heating system

Bahnhof's model could be replicated in cities where there are municipal hot water systems - Scandinavia, Russia and Canada. But even where these are lacking, it may not be necessary for data centres to throw their excess heat away. Data centres could be used to heat swimming pools, greenhouses and university buildings, says Peter Hopton, founder of the British company Iceotope. Using a patented liquid cooling technology, Iceotope have been powering the radiators in one computer lab at the University of Leeds for the last couple of years.

You're having the world's largest internet retailer essentially heat their back office space with the waste heat from the internet Richard Stevenson, Clise Properties

A similar idea - on a much grander scale - is about to take place in Seattle. From the outside, the Westin Building looks like a regular office building, but inside it's essentially a giant switchboard. As one of the country's four "gateway telco-hotels", the building patches transoceanic telecommunications through to local networks, linking the US to the outside world. "This particular office building was designed as an office building and never as data centre and over the last 20 years has been slowly converted to being this gateway hotel," says Richard Stevenson, president of Clise Properties, which owns the building. "And as a result it's probably one of the five largest users of electricity in the Seattle area."

The waste heat currently gets pumped up to the roof and released into the air.

Clise also owned a large plot of land across the road from the Westin, which it sold to Amazon in 2012. The online retailer is now in the process of building three 38-storey office towers, which will encompass more than three million square feet of space. Once complete, Amazon's headquarters will be the largest in any North American city.

As plans for the project took shape, Richard Stevenson saw an opportunity to make his operation at the Westin Building a little greener. "I was talking to an engineer by the name of Jeff Sloan at McKinstry and Company," he recalls. "And I said, 'You know it's kind of a shame that we're always dumping this heat in the atmosphere - isn't there some way we can sell it to these guys?' And he kind of looked at me and went, 'Well, yeah.'"

Image copyright Clise Properties Image caption The Westin Building, centre, is a familiar sight on the Seattle skyline

Image copyright Clise Properties Image caption The pipes that will soon take the Westin's excess hot air across the road to the Amazon HQ

Builders are now laying the pipes that will take hot water from the Westin building on a loop through Amazon's new campus, where it will be used to heat around three-quarters of the office space. "To me it's very cool because you're having the world's largest internet retailer essentially heat their back office space with the waste heat from the internet," says Stevenson.

Since getting his Nerdalize radiator, Jerry van Waardhuizen has become more aware of the issue of heat retention. "In my company we have some servers," he says. "We put on an air con above it - we give a lot of money to destroy the heat. That's crazy! That's crazy! Everybody is doing that."

At home though, he likes to leave his new radiator on, open the doors, and let the warm air waft over his garden. It makes no difference if it is expelled that way, he explains, rather than through the extractor fitted to the back of the unit.

It is a treat for this eco-conscious man to be able to sit outside on a May evening in Rotterdam without a jacket. Instead of feeling guilty about wasting energy, he says he likes to muse on the problems his radiator might be working on.

Florian Schneider spoke to Click on the BBC World Service. Listen to the interview on BBC iPlayer or get the Click podcast.

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