How Water Heaters Work

Let's take a quick look at the inner components that work together in your water heater to make your morning shower so satisfying:

Now, let's see how all these parts work together to provide you with hot water.

Let's take a close-up look at what's going on inside a water heater's tank to see how it does its job.

A water heater's thermostat controls the temperature of the water inside the tank. Normally, you can set the temperature anywhere between 120 and 180 degrees Fahrenheit (49 to 82 degrees Celsius). The water temperature setting recommended by most manufacturers is between 120 to 140 degrees Fahrenheit (49 to 60 degrees Celsius). This is hot enough to be sufficient for household use, but not hot enough that it can pose a scalding risk. If there are children living in your home, it's wise to stay closer to the lower end of the range.

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 dip tube feeds cold water from your home's water lines to the bottom of the tank's interior, where the water starts to warm up. The heating mechanism — either a burner or an element — stays on until the water reaches temperature.

As the water heats, it rises to the top of the tank. The heat-out pipe is located near the top of the tank. Water exiting the water heater at the top is always the hottest in the tank at any given moment because it's the nature of hot water to rise above denser, cold water.

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.

Home improvement experts recommend performing preventative maintenance annually on tank-style water heaters, which a professional technician can help you with. Components such as the pressure release valve and anode rod should be inspected to ensure effective operation.

Over time, the tank can also fill up with natural sediment and minerals from your water source. These contaminants clump together at the bottom of the heater, reducing its efficiency and potentially shortening the service life of the system. To stop this from happening, the technician can drain the tank and flush out any collected sediment.

Although tank style water heaters are still very popular, especially in the U.S., tankless water heaters are gaining in popularity. Where a tank-style water heater continuously heats the water to make it available when you need it, a tankless system creates hot water on demand. Tankless heaters sit idle most of the time, and are automatically switched on whenever hot water is needed.

These provide less gallons-per-minute of hot water than a typical heater, and can take a while to warm up. However, they also use nearly zero energy when hot water is not needed. By comparison, the traditional system will keep switching itself on to maintain the heat in its tank, even when no one is home.

Although this can mean big energy savings, a tankless system can initially cost up to three times as much as a standard water heater setup. Multiple water heaters will also likely be required to effectively provide hot water for multiple bathrooms and appliances. On the other hand, energy savings will go back into your pocket in the long run, and there are often incentives like tax rebates that go toward the installation of high-efficiency heaters.

Other types of efficient heaters are used in more niche applications, such as solar heating systems. These use a series of water-filled pipes installed along the roof of a building. These pipes collect the natural heat of the sun and then transfer the hot water into an insulated collection tank using pumps or gravity flow. In the process, the system uses very little energy, but it requires a warm, sunny climate and a lot of roof space.

There are drawbacks, as cold weather can cut off the whole hot water supply. It also takes a long time to replenish the storage tank if it is drained completely. Many solar water heaters will also include an electrical or gas heating method as a backup, which helps alleviate the disadvantages.

Geothermal water heaters work similarly to their solar counterparts, but instead use pipes buried underground. In areas of volcanic activity, geothermal heaters can take advantage of the reliable and practically infinite heat that radiates from the Earth's core.

Originally Published: Apr 1, 2000