A water heater heats water with a gas burner or electric element in a tank and holds it until you use it.
Tank type
- A burner (gas) or heating element (electric) heats water in an insulated tank.
- A thermostat keeps it at around 120°F.
- Hot water leaves from the top through a dip tube.
Tankless
Heats water on demand as it passes through a heat exchanger.
Capacity
Residential tanks hold 40 to 50 gallons.
Lifespan
8 to 12 years for tank units. 20 for tankless.
Safety
Set to 120°F to prevent scalding.
Tank water heaters
A storage tank holds 30 to 80 gallons of water. Gas models use a burner at the bottom, and electric models use heating elements. A thermostat keeps the water at the set temperature, usually 120 degrees F (49 degrees C), which the Department of Energy recommends to reduce scalding and energy use. Cold water enters through a dip tube near the bottom, and hot water leaves from the top.
Anode rod
A sacrificial magnesium or aluminum anode rod attracts corrosive elements to protect the tank. Replace it every 3 to 5 years to extend life.
Tankless heaters
They heat water on demand with a gas burner or electric element as water flows through a heat exchanger. They provide continuous hot water and save space. Flow rates of 2 to 5 gallons per minute are typical, and large homes may need multiple units.
Heat pump water heaters
They move heat from the air to the water and use about 60% less electricity than standard electric heaters, according to the Department of Energy. They qualify for federal tax credits and often rebates.
Safety valve
The temperature and pressure relief valve opens if the temperature or pressure becomes too high. Test it yearly.
Lifespan
Tank heaters last 8 to 12 years, tankless 20 years or more, and heat pump 10 to 15 years.
Maintenance
Flush the tank annually to remove sediment. Check for leaks and rust.
Energy
Water heating uses about 18% of a home’s energy, the second largest energy expense after heating and cooling.
Legionella
Keep tank temperatures at 120 degrees F or higher at the heater to limit the growth of Legionella bacteria, and use a thermostatic mixing valve at taps to prevent scalding.
Tank, tankless and heat pump types
A conventional tank water heater stores 30 to 80 gallons, commonly 40 or 50, and heats it with a gas burner or electric elements controlled by a thermostat. The Department of Energy recommends setting the temperature to 120 F to save energy and reduce scald risk. A tankless heater heats water on demand as it flows, delivering about 2 to 5 gallons per minute, and lasts around 20 years. Heat pump water heaters move heat from the air into the tank and can be about three times as efficient as standard electric models.
Safety and maintenance
An anode rod, made of magnesium or aluminum, corrodes in place of the tank and should be checked every 3 to 5 years. A temperature and pressure relief valve opens if pressure or temperature gets too high and should never be blocked. Tank heaters last about 8 to 12 years, and flushing the tank annually removes sediment. Legionella bacteria grow in water between about 77 and 113 F, so storing water at 120 F or above reduces risk. Signs of failure include rusty water, rumbling noises, leaks at the base and lack of hot water.
Based on data from the US Department of Energy and the CDC
