Anode Rod

A long metallic rod that’s screwed into the top of the hot water heater that, through a process of electrolysis, slowly degrades over time to protect the other metallic parts, and must be replaced every four to six years.


The gas flame in the hot water heater that heats up the water.

Circuit Breaker

In most modern homes, the system used to protect electrical systems against power surges or other electrical issues. Electrical hot water heaters have their own separate breaker on the panel.

Cold Water Inlet

The incoming water supply for the heater, normally located near the top of the appliance.

Cold Water Shut-Off Valve

A valve on the cold water inlet used to manually shut off the water when the heater is in need of repair or replacement.

Dip Tube

An extension onto the cold water inlet that ensures new unheated water is deposited at the bottom of the tank, allowing already-heated water to rise to the top for use.

Electric Water Heater

A hot water heater that uses electricity to heat water, as opposed to other power sources such as gas or coal.


A piece of metal that is heated using electricity, such as on a stove or in a water heater. Most electric water heaters have two elements, at the top and bottom of the appliance.

Gas Water Heater

A hot water heater that uses a natural gas flame as a power source, as opposed to other power sources such as electricity or coal.

Heat Exchanger

A piece of equipment designed to transfer heat from where it’s produced to where it’s needed while minimizing waste energy. Tankless water heaters use heat exchangers to quickly heat the water as it passes through the device.

Heater Drain Valve

A manual tap or valve near the bottom of the hot water heater. This can be used to drain the tank for disposal or to remove sediment.

 Hot Water Outlet

The pipe near the top of the heater from which heated water leaves the tank.


A material used to reduce the rate of heat transfer (i.e. to keep hot things hot and cold things cold). Tank-style water heaters are wrapped in insulation.

On/Off Control

All heaters have some form of the control system to turn the machine on and off. This may be part of, or separate from, the thermostat. On electrical heaters, on/off control is sometimes only possible by flipping the circuit breaker.

Pilot Light

In gas-powered heaters, this is a small flame that is always on, allowing the primary heater to kick in without an additional ignition source.


Calcium and other minerals and particulate matter that exists naturally in the water supply, but may begin to build up over time in a water heater. Sediment build-up can have serious effects on the capacity and efficiency of the water heater, blocking up pipes and logging machinery. Sediment can be dealt with by flushing out your heater once a year.

Storage Tank

On standard model heaters, a large tank is used that is always full of already-heated water.

Tankless Water Heater

Some models of water heater, instead of keeping a storage tank of water at the ready, consist of a series of pipes and a heat exchanger. Water enters the system as needed, is rapidly heated up, and is then sent on its way. Tankless water heaters can take longer to heat up, but they will never run out of hot water.

Tank-Type Water Heater

This is the most common type of water heater, utilizing a cold water inlet to bring water into a large, heavily insulated storage tank. The water is then heated (normally using either gas or electricity as a heat source) and then stored until needed, at which point it exits through the hot water demand.

Temperature and Pressure Relief Valve

As water is heated in the tank, steam can be generated, causing excess pressure that, in the sealed environment of the storage tank, could lead to a disastrous collapse. Modern water heaters are fitted with relief valves that sense these pressure spikes and automatically vent excess steam. This is normally on top of the heater, with a plastic tube for the vented steam.


The control mechanism used to adjust the temperature of the water within the heater. This is normally located adjacent to the heating element – so near the bottom of the heater on gas heaters, and in two locations, the bottom and the top, for electric heaters. If there are two heaters, both should be set to the same temperature, so the two heating elements are not working at cross purposes.

Venting System

In the case of gas powered furnaces, a venting system must be used to deal with waste gases from the combustion process. This system generally vents directly to the outside, and, in the case of high-efficiency gas-powered furnaces, may be aided by an electric motor.

A Water Heater Dictionary with Pictures