Water heaters are familiar fixtures in most homes. They typically look like big metal cylinders, tall drums that are often consigned to a laundry room or basement. Newer styles have some interesting features, like losing the tank completely in favor of water-on-demand, but the old, reliable water heater design that’s most widely used in the U.S. today is really a pretty simple appliance; it’s basically a drum filled with water and equipped with a heating mechanism on the bottom or inside. Even though they lack drama and complexity, water heaters are still pretty amazing. What makes them interesting is that they exploit the heat rising principle to deliver hot water right to your faucet with a minimum of fuss. Don’t let the simple shape shrouded in its wooly insulating blanket fool you. Water heaters have an ingenious design on the inside for something that looks so ordinary on the outside. Setting your water heater to a lower temperature saves energy, too, and if you remember to dial back the heat when you go on vacation, you’ll experience even more energy savings. Usually, the thermostat is located underneath a protective cover plate and has a knob or dial you can turn to set the temperature. The secret to a water heater’s design for separating cold, incoming water from hot, outgoing water is that it relies on the principle that heat rises to do the hard part. The position of the heat-out pipe at the top of the tank does the rest.