The words “efficiency” and “government” rarely belong in the same sentence. There is one government entity that is an exception to the rule, and despite being a place known for its secrecy, it is more than willing to share this particular secret.

The Central Intelligence Agency (CIA) is the most secretive agency in the world. Among the many techniques employed by America’s spymasters is the practice of not only shredding classified documents but also burning them. “Burn after reading” is the designation placed on the most sensitive materials. Once the purpose of the document has come to an end, the Agency first shreds all of the pages. To avoid reassembly by skilled jigsaw puzzle enthusiasts, the shredded documents are destined for the incinerator, where the flames remove the last of the secrets.

As you can imagine, the CIA destroys a lot of documents, keeping the incinerator burning around the clock. Rather than let all of that heat go to waste, the Agency came up with an inspired environmental solution. The energy from the burning documents is used to heat the building’s hot water.

In an Earth Day press release on April 22, 2011, the Agency reported:

In addition to saving fuel, that process reduces the amount of waste–which would otherwise be destined for landfills–by nearly 1,000 tons per year. The CIA increases its recycling efforts each year, annually collecting over three tons of plastic, glass, cardboard, aluminum, construction debris, and other waste.

The CIA also pointed out that their most recently built facilities have a Gold LEED rating from the U.S. Green Building Council and “consume over 20 percent less energy and approximately 40 percent less water than typical buildings of the same size and use.”

This practice, along with the most exclusive Starbucks in the world, makes the pleasant experience of working at CIA Headquarters an open secret.

Read about the inventor of some of the most environmentally-unfriendly products ever.

Read more fun facts about espionage.