In 2004, ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommended an operating temperature range from 20°C to 25°C. In 2008, the society went further, suggesting that temperatures could be raised to 27°C.

Following that, the society issued Revision A1, which raised the limit to 32°C (89.6°F) depending on conditions.

This was not an idle whim. ASHRAE engineers said that higher temperatures would have little effect on the lifetime of components, but would offer significant energy savings.

Figures from the US General Services Administration suggested that data centers could save four percent of their total energy, for every degree they allowed the temperature to climb. //

Facebook quickly found it could go beyond the ASHRAE guidelines. At its Prineville and Forest City data centers, they raised the server temperatures to 29.4°C, and found no ill effects. //

Google went up to 26.6°C, and Joe Kava, then vice president of data centers, said the move was working: “Google runs data centers warmer than most because it helps efficiency.”

Intel went furthest. For ten months in 2008, the chip giant took 900 servers, and ran half of them in a traditionally cooled data center, while the other 450 were given no external cooling. The server temperatures went up to 33.3°C (92°F) at times.

At the end of the ten months, the chip giant compared those servers with another 450 which had been run in a traditional air-conditioned environment. The 450 hot servers had saved some 67 percent of the power budget.

In this higher-temperature test, Intel actually found a measurable increase in failure. Amongst the hot servers, two percent more failed. But that failure rate may have had nothing to do with the temperature - the 450 servers under test also had no air filtration or humidity control, so the small increase in failure rate may have been due to dust and condensation.