Sitting in our climate-controlled homes, it's easy to forget how humans tried to beat the heat for most of our history: With good old-fashioned hand fanning and sweat. Despite these and other primitive efforts to cool down, it was heat that always beat us — until air conditioning came along.
Air conditioning started off as an industrial tool before it slowly worked its way into the home. The story begins in 1902 when a young engineer named Willis Carrier (that last name should sound familiar) invented a system to control the humidity in his employer's printing plant by passing air through water-cooled coils. By 1922 Carrier had improved the design, making it small, efficient, reliable and affordable enough to be installed in movie theaters across the country. Soon the technology spread to office buildings, department stores and rail cars, but not so much in homes; by 1965 only 10 percent of American homes had air conditioning [source: Oremus]. Lower cost units eventually boosted that number to 87 percent by 2009 [source: U.S. Department of Energy].
The impact of air conditioning on American life has been huge. At work, the comfort it provides has helped to increase our productivity. It's also changed the way we build our homes, by reducing the need for high ceilings and operable windows. And it's changed where we live, too: Places like Arizona and Florida boomed with the availability of air conditioning [source: U.S. Department of Energy].