Recycling heat is actually quite simple. For example, new buildings often have condensing water heaters, which use gas burners to warm up water (just as other heaters do) but also capture the heat in the combusted gas that’s going out the flue. It happens on a larger scale, too. In 1882, when Thomas Edison built the world’s first commercial power plant in Manhattan, he sold its steam to heat nearby buildings. Today, such plants are known as combined heat and power, or cogeneration, plants. Edison’s old plant eventually became the massive Con Edison, whose operations today produce 19.7 billion pounds of steam a year. The ArcelorMittal steel mill in East Chicago, Indiana, is another good example. It uses extra blast furnace heat to make steam that then generates electricity for the mill, saving roughly $20 million a year and preventing 340,000 tons of carbon dioxide emissions—the equivalent of taking 62,000 cars off the road.