Understanding How Your Hot Water Heater Works

You may not think much about your hot water heater, and it’s easy to see why. All you have to do is turn on the tap and the water instantly makes its way to you. In reality, the process isn’t so simple. Your hot water heater is a complex machine that goes through an intricate process whenever you want to wash your hands or run a bath. Here’s the inside scoop on how your hot water heater works.

The mechanics of a hot water heater

The inner workings of your hot water heater are complicated, but not impossible to understand. Here’s an overview of the main parts that keep your hot water heater up and running:


The largest component of your hot water heater is the tank. The tank of a hot water heater is a large outer shell, typically located in a garage, closet, or otherwise away from the main living area. The average tank holds between 40 and 60 gallons of water. Tanks are lined with some sort of insulating material, since as poly urethane foam, to help them heat water more efficiently.

There are two types of tanks: Gas, otherwise known as fuel-fired, and electric. 60% of the homes in the U.S. use gas heaters, while the remaining 40% use electric or solar powered heaters. While a gas tank has a vent at the top to remove exhaust gas, an electric tank simply has a cable that connects the heater to the home’s electric panel. Gas heaters are generally less energy-efficient than electric heaters, but they have a much faster recovery rate. This makes them a convenient option for larger families who need large amounts of hot water in shorter periods of time.

Tankless water heaters are an alternative for homeowners who don’t have room for a large tank. Tankless water heaters also work faster than traditional heaters, due to the fact that the water is heated on-demand and not in a tank.

Dip tube

This tube, located at the top of the tank, serves as the entry point for water as it flows into the tank. The water then travels to the bottom of the tank, to the area known as the combustion chamber, where the heating process begins.

Dip tubes generally last as long as the hot water heater they’re attached to, and aren’t prone to problems. However, if there is a crack or break in the dip tube, cold water entering the tank can cool down the hot water that’s about to exit the tank. This results in lukewarm water being sent through your pipes when you want hot water. Any problems with a dip tube can be identified by a plumber during a water heater inspection.


Just as the thermostat in your home allows you to adjust a room’s temperature, your hot water heater’s thermostat controls the temperature of the water inside the tank. Many manufactures set the thermostat to 140 degrees Fahrenheit by default. For most households, lowering the temperature to 120 degrees Fahrenheit produces a sufficient amount of hot water. Lowering the temperature can also potentially result in lower energy bills, and a longer lifespan for the heater overall.

Pressure relief valve

A pressure relief valve is a safety measure that keeps the pressure inside the tank from exceeding around 50 to 100 pounds per square inch. If the pressure becomes dangerously high, the valve opens to release pressure buildup and prevent a dangerous explosion. Mineral salt, rust, and corrosion can all block the valve from draining correctly. If the valve can’t relieve pressure because of blockages, the water heater is at risk of exploding. You should test your pressure relief valve to ensure water runs out of it and doesn’t seem to be blocked by anything inside the tank. If you suspect a blockage is present, call a plumber right away.

Leaks are another sign of trouble when it comes to pressure relief valves. If you notice that the valve is leaking, you should call a plumber immediately. Leaks indicate that the valve isn’t functioning correctly, creating a dangerous scenario where the water in the tank could exceed its boiling point. This could result in scalding hot water endangering your unsuspecting family members when they turn on a faucet.

Drain valve

As the name suggests, a drain valve allows water to drain out of the tank. A drain valve is an essential part of flushing the tank of your water heater. Flushing your heater is your best defense against the buildup of calcium, lime, and bacteria that can wreak havoc on water lines and reduce energy efficiency. Due to Arizona’s notoriously hard water, these problems are an even bigger deal. You should flush your water heater through the drain valve at least once a year.

Sacrificial anode rod

Iron, oxygen, and water are all prone to rust, and since all three are present in a hot water heater, a sacrificial anode rod is used to prevent the tank from rusting. An anode rod is made of aluminum or magnesium. Due to the chemistry of these metals, they rust faster than the metal used to build the tank. With the anode rod attracting all of the rust, the tank itself and the water inside it are kept safe. This is where the rod earns the name “sacrificial”, as it sacrifices itself to rust away for the sake of the water in the tank.

An anode rod typically lasts up to three years. It’s important to have your anode rod replaced before its lifespan is up. Once the rod has rusted away completely, the tank itself will begin to rust, which can cause water heater failure. Rust in the tank can also cause your water to have a vague sulfur smell and taste.

The hot water process

Now that you know the main parts of a hot water heater, you can visualize how they all work together to deliver hot water when you need it:

Water travels through your home’s water lines and then enters the tank through the drip tube. Once the water reaches the bottom of the tank, the heating mechanism turns on and heats the water until it reaches the temperature on the thermostat. As it heats up, the water rises to the top of the tank and into the heat-out pipe. From the heat-out pipe, the water enters your home to be routed to whichever appliance or fixture needs it. The pressure relief valve maintains a steady pressure inside the tank while all this is going on, to protect your heater from an explosion.

Trust Chas Roberts as your water heating experts

With over 75 years of experience, there’s no water heater problem we haven’t seen before. Whether you’re disappointed by lukewarm showers or can’t figure out why your heater keeps breaking down, contact us for the answer.