How Your Water Heater Works – Part 1: Storage Tank Water Heaters

Storage tank water heaters, familiar fixtures in many homes, are the most common type of water heater. Typically looking like tall drums, they are often relegated to a laundry room, basement, or other out-of-the-way corner of your home. But as you take that hot shower in the morning, did you ever stop and think about exactly how that hot water gets to your showerhead? Generally speaking, the most common water heaters can be classified as either “storage tank water heaters” or “tankless water heaters.” In this post, we examine the former.

In a traditional system, there’s a large tank that holds and heats water. It’s basically a container filled with water and equipped with a heating mechanism inside or underneath. To make sure you have a ready reservoir when you need it, the tank continually heats the water to maintain a constant temperature.

To start the process, the dip tube carries the cold water from your water lines to the bottom of the tank. With the tank full of water, a heating mechanism, either a burner or an element, engages until the water reaches the desired temperature. There are several fuel sources for storage heaters, including heating oil (or B5 Ultra Clean), propane, electricity and natural gas.

As the water in the tank heats up, it rises to the top. A thermostat controls the temperature of the water inside the tank. Normally, you can set the water temperature anywhere between 120 and 140°F. However, most manufacturers recommend temperatures around 120 – hot enough to be efficient for household use, but not so hot that it can pose a scalding risk. Finally, the heat-out pipe is located near the top of the tank. As hot water is released through the heat-out pipe to your home, more cold water enters the bottom of the tank, ensuring that the tank is always full.

Separating the cold, incoming water from hot, outgoing water is the secret to a water heater’s design. Of course, the “secret” isn’t really much of a secret at all: it’s basic science. The water exiting the heater at the top is always the hottest water in the tank because it’s the nature of hot water to rise above the denser cold water. The heat-out pipe at the top of the tank takes care of the rest, sending the hot water on its way to your shower, dishwasher, or faucets. And if your storage tank water heater is maintained properly, you can count on this process to work reliably for about 10 years – the average lifespan of a typical storage tank water heater.

Of course, you also have the option of going “tankless,” and we’ll take a look at tankless water heaters in Part 2 of this series.