What Is a Water Heater?

By Mark Soto

October 13, 2025

A water heater is a home appliance that heats up cold water and then stores it to provide warm water for daily usage for showers, laundry and dishwashing. There are many types of water heaters, including tank and tankless systems, as well as electric and gas-powered models.

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Since it’s such an important component of your home for comfort, you’ll want to be familiar with water heaters and know what their functions are and the different types.

How Does a Water Heater Work?

A water heater receives water from your home through the cold water inlet found near the top of the heater. The water is then heated up using your specific type of energy mechanism. If you have an electric water heater, it heats up the water by passing electricity through its coils, which creates resistance and produces heat. For gas water heaters, the water is heated up by a gas burner below the tank, whose flame heats up the water through the central flue pipe.

Water Heater Temperature

You can adjust the water temperature on your water heater to match your preference, but most heaters come set at the recommended default of 120 degrees Fahrenheit, per the Department of Energy. Too low, and your water heater can harbor dangerous bacteria.. Too high, and you can scald yourself while washing the dishes.

What Do Water Heaters Look Like?

You can find your water heater in your basement, crawlspace, garage or even outdoors. Tank water heaters look like large cylinder tubes of water with connections to your home for the gas line, water line or electrical connection. Tankless water heaters are much smaller, since they don’t need to store any water. Tankless heaters look more like rectangular boxes that are installed along your wall.

What Are the Different Types of Water Heaters?

There are two main types of water heaters: tank and tankless systems. Tank water heaters, also known as conventional water heaters, store the water that they heat up in a tank with tank sizes measuring 20, 30, 40, 50, 60, 70 and 80 gallons. You can even find bigger sizes that can hold up to 120 gallons of water. This water is stored and maintained warm, so that when you need running hot water, you’ll get it on delivery. As soon as warm water leaves the system, it receives cold water and heats it up so that it doesn’t run out.

How Tankless Water Heaters Work

In a tankless water heater system, the heating methods are the same as with traditional, tanked models. The only difference is that the water is heated as you need it, rather than stored hot in a tank.

Tankless water systems have a gallons per minute (GPM) rating, which showcases how much warm water they can deliver within a minute. You’ll need to calculate the rating you need based on how much water you might require within a single instance. For example, if you wash the dishes while someone takes a shower, you’ll want a tankless water system that has a sufficient rating to handle delivering hot water to both places at the same time. GPM ratings range from 3.25 gallons to 7.0 or higher.

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Are Water Heaters Gas or Electric?

Water heaters can be gas, electric and even solar. The main difference between gas and electric water heaters is the energy they use to heat up your water. Gas water heaters use a gas flame to heat up the water. Electric water heaters pass electric current through coils, which create resistance that produces heat and warms up the water. In terms of costs, gas heaters cost less to run than electric heaters since gas is on average cheaper than electricity. However, when purchasing a system, you’ll find that the electric systems are cheaper to buy and install due to their easier setup. Gas heaters also don’t last as long as electric systems, with lifespans ranging from 8 to 10 compared to 10 to 15 years for their electric counterparts. Gas tanks can heat up your water faster, so if you have a smaller tank that runs out of water, you’ll get a faster recovery rate with a gas one than an electric one.

How Do I Know If My Water Heater Is Gas or Electric?

Gas water heaters are connected to gas lines, so look for those running into or out of your machine. Gas water heaters also have a pilot light — a literal burning flame — down near the bottom of the unit. If you have an electric model, you may see wiring isntead of these features.

What to Know About Solar Water Heaters

Solar water heaters employ the power of the sun to heat up water. That heated water is stored in a tank until it is used. These are often installed on roofs to take advantage of the sunlight. Often, these aren't the home's only source of hot water (due to low storage capacity and the time it takes the sun to heat up the water). Homeowners may also have a small tanked or tankless model inside the house as well.

Water Heater Maintenance

To keep your water heater working efficiently, you’ll want to keep up with the maintenance for it. Maintenance will vary depending on whether you have a tank or tankless system but they share similar steps.

Water Heater Flushing

For tank water heaters, the main thing you really want to do is get them flushed at least once a year. When water enters the tank and gets heated, it will release minerals that start to build up at the bottom of the tank. This sediment that builds up eventually starts to grow larger and forms it’s own layer at the bottom. Since most of the heating occurs from below the tank, it becomes less efficient when the heating element has to warm up the water through the sediment layer. When you flush the heater, you drain out all of the water and remove the sediment.

Water Heater Descaling

For tankless systems, the process is called descaling but it’s similar to flushing. You just remove the sediment from the heat exchanger instead of removing it from the bottom of the tank since it won’t have one. Apart from that, you’ll also want to clean the inlet filter every 6 months.

Your Water Heater Could Use a Professional Touch

Regular water heater tune-ups can keep your hot water systems running optimally throughout the year. They can also serve to extend the lifespan of your equipment. While descaling or flushing is a task many homeowners can handle on their own, you don't have to. A plumber can take this task off your hands for you, if you wish. It's also important to note that the manufacturer's warranty on your machine moght require professional service only.

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