This article focuses on traditional storage (tank) water heaters. For an overview of both tank and tankless systems, see How a Water Heater Works (Tank & Tankless).
A storage tank water heater heats and stores water for use throughout your home. This guide explains how traditional tank systems work and how they differ from tankless units. Unlike tankless water heaters, storage systems keep a ready supply of hot water but can run out if demand exceeds capacity.
Quick Answer
How a Water Heater Works
Gas Water Heaters
Electric Water Heaters
Key Parts of a Water Heater
Maintenance Basics
FAQs
Understanding how a water heater works can help you troubleshoot problems, improve efficiency, and extend the life of your system.
Quick Answer
A storage water heater heats water inside a tank using a gas burner or electric heating elements. Cold water enters through a dip tube, heated water rises to the top, and hot water is delivered to faucets when needed.
How a Storage Water Heater Works
A water heater is connected to a cold-water supply and a hot-water distribution system. As hot water is used, cold water enters the tank and is heated.
- Cold water enters through a dip tube
- Heat is applied inside the tank
- Hot water rises to the top
- Hot water exits to fixtures when needed
Because the tank is pressurized, hot water flows out immediately when a faucet is opened.
How a Gas Water Heater Works
Gas water heaters use a burner located beneath the tank to heat water.
- A thermostat controls gas flow to the burner
- A pilot light or electronic ignition starts the burner
- Hot exhaust gases vent through a flue
High-efficiency models may use power vents to exhaust gases through a wall instead of a chimney.
How an Electric Water Heater Works
Electric water heaters use heating elements inside the tank.
- Electric elements heat water directly
- Thermostats control each element
- No venting is required
Most units use one or two heating elements, depending on capacity and recovery speed.
Key Parts of a Water Heater
Understanding these components helps with troubleshooting:
- Dip tube: Directs cold water to bottom of tank
- Heating element or burner: Heats the water
- Thermostat: Controls temperature
- Anode rod: Prevents tank corrosion
- T&P relief valve: Releases excess pressure
- Drain valve: Used for flushing sediment
👉 See Water Heater Pressure Relief Valve for safety details.
Water Heater Maintenance Basics
Regular maintenance helps extend the life of your water heater:
- Flush sediment from the tank once or twice a year
- Test the temperature-pressure relief valve
- Inspect the anode rod periodically
👉 See Water Heater Troubleshooting Guide for diagnosing issues.
FAQs
How does a water heater heat water?
It uses a gas burner or electric elements to heat water stored in a tank.
Why does hot water run out?
This happens when the tank’s stored hot water is depleted faster than it can be reheated.
How long does a water heater last?
Most tank water heaters last 8 to 12 years.
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