Most homeowners in the United States probably don't devote much thought to their heating system. You just flip a switch, set the thermostat and enjoy a warm, snug home, safely insulated from winter chills. Aside from some annual maintenance and occasional repair, it's the picture of convenience. It hasn't always been that way, however -- read on for a whirlwind tour of human home heating over the years.

In the Beginning

In prehistory, heating the home was a simple, if dirty and labor-intensive affair -- just build a fire in the cave. Researchers have found evidence that humans have built fires for at least 1.2 million years, according to an article on Hankering for History. Hearths specifically built for fires go back at least 45,000 years ago, and then were improved again tens of millennium later with the invention of the chimney in the 14th century. Stoves came around in the 17th century, but fireplaces remained the primary form of home heating until a fellow named Benjamin Franklin invented a safer, more efficient stove in 1741, a variation of which still bears his name today.

The Reign of King Coal

While we transitioned from fireplaces to stoves, wood reigned unchallenged as humanity's main source of heat until coal entered the picture. Around 1885, coal surpassed wood as the nation's primary fuel. Coal carts and later, trucks, would deliver piles of the fossil fuel to basements across the country, where early versions of the furnace burned it and then distributed heat throughout the house.

Other heating fuels gradually made their way onto the market -- gas stoves came about in the first half of the 19th century, while oil heaters appeared in the 1920s. But the old ways were still the most popular: According to the U.S. Census, 75 percent of homes still used wood or coal as their primary heating fuel in 1940. Even today, although coal has finally fallen out of favor for household use, the country mines almost one billion tons annually, 90 percent of it destined for electricity-generating power plants.

Today: Boundless Options

Homeowners of the 21st century have their choice of modern, efficient furnaces and boilers fueled by natural gas, electricity, oil or propane. Today, 57 percent of American homes use natural gas, by far the dominant fuel. About 10 percent use propane or oil, with most of the remaining homes using electricity as their primary means of heat.

And the earliest heating fuel, wood, is still around. Some families use modern, efficient woodstoves, while other innovators have taken wood heating to the next level with rocket mass heaters.

On the other end of the spectrum, among the most modern and efficient heating equipment available to consumers are heat pumps, both air-sourced and geothermal. Heat pumps work by taking advantage of the difference between your indoor air, and either the air outside or the temperature underground. Couple innovation like that with a smart thermostat, which automatically looks for energy savings in your heating system, and think of how far we've come from the days of building a fire in the cave to stay warm.

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