170. How does a steam heating system work?
A home steam heating system consists of a boiler, pipes, and radiators. The boiler is located in the basement and uses a burning fuel or electricity to heat water until it boils. Steam forms as the water boils and this steam accumulates above the liquid water. Steam isn't the mist that forms above a teapot—that's really just droplets of water. Steam itself is the clear gaseous form of water and it travels upward through the pipes to radiators in the rooms. Steam is actually a lighter-than-air gas and it's lifted upward by the same buoyant force that makes helium float. When the steam arrives inside the radiators, it begins to condense back into liquid water. As it does so, it releases an enormous amount of heat—the water molecules begin to stick to one another and they release chemical potential energy. After a short time, the temperature of the radiator rises until a balance is reached where the steam and the water are in equilibrium—typically about 100° Celsius, but dependent on the gas pressure inside the radiator. The hot radiator then heats the room. The water that forms as the steam condenses is carried by gravity back down the same pipe through which the steam arrived and returns to the boiler to be reheated.