See how your water heater works.

This example shows a conventional atmospheric gas tank: a burner below the vessel adds heat, while combustion gases travel through a central flue toward the outdoor vent. Other gas water heaters use different combustion and venting arrangements.

Tank & insulation

The inner tank contains water under pressure. Its lining helps protect the steel, while surrounding insulation slows heat loss between uses.

Cold in, hot out

The dip tube directs incoming cold water toward the bottom. Hot water leaves from the upper part of the tank as a fixture draws water.

Burner & gas control

The gas control responds to water temperature and governs fuel delivery. The burner releases heat inside the combustion chamber when the controls call for heating.

Flue & draft hood

In this atmospheric design, gases rise through the central flue and draft hood into the vent. The venting arrangement is part of the appliance's safe operation.

Corrosion & pressure protection

A sacrificial anode helps limit tank corrosion. The temperature-and-pressure relief valve can release water when its temperature or pressure limit is exceeded.

This example uses upper and lower resistance elements in an insulated storage tank. Thermostats control heating as water is used and replenished. There is no gas burner or combustion flue in this electric design.

Tank & insulation

The inner vessel holds water under pressure. Insulation around it reduces heat loss; the exterior jacket covers the assembly.

Cold in, hot out

An internal dip tube carries incoming water downward. The upper outlet supplies the home as water is drawn.

Upper & lower heating elements

The two submerged elements add heat at different heights. Their operation follows the heater's control design; other electric models may have a different arrangement.

Thermostats & high limit

Thermostats respond to water temperature. A separate high-temperature cutoff interrupts heating if an overheating condition occurs.

Anode & relief valve

The sacrificial anode helps protect the tank against corrosion. A temperature-and-pressure relief valve provides separate protection from excessive temperature or pressure.

The fan, evaporator, compressor and condenser work together to move heat into the tank. This illustrated hybrid also has resistance elements for additional heating when its controls call for them. The room, demand and operating mode affect performance.

Insulated storage tank

An insulated water vessel sits below the heat-pump assembly. Its stored supply and reheating capacity work together to serve the home.

Fan & evaporator

The fan draws air across the evaporator. Refrigerant absorbs heat there, so outgoing air is cooler; moisture can also condense from that air.

Compressor

The electrically driven compressor raises the temperature of refrigerant vapor so it can transfer heat to the water. Refrigerant stays within a separate sealed circuit.

Condenser coil

This example uses a coil around the tank wall to transfer heat into the water. The refrigerant and drinking water remain separate; other designs arrange the heat exchanger differently.

Supplemental electric elements

Upper and lower elements provide another source of heat. Whether they run depends on the appliance, selected mode, conditions and demand.

Controls & tank protection

The controller uses sensor information to manage the available heating sources. The tank also needs temperature-and-pressure protection independent of its everyday operating mode.

This representative condensing tankless heater shows two stainless-steel heat exchangers, controlled combustion and a flowing-water path. Hot-water output depends on the required temperature rise and demand. Component arrangements vary by equipment.

Cabinet & support frame

The front cover and chassis surround the internal equipment. The model separates them only to explain the appliance; actual equipment stays closed during normal use.

Combustion fan & burner

A powered fan supports combustion airflow, and the burner supplies heat. Intake and exhaust connections are distinct parts of the combustion system.

Dual stainless-steel heat exchangers

The primary exchanger transfers combustion heat to water. The secondary exchanger recovers additional exhaust heat, cooling the gases enough for water vapor to condense.

Water connections & flow sensing

The cold inlet, internal water path and hot outlet connect the heater to the home. Flow sensing gives the controls information about water demand.

Electronic controls & display

The control board coordinates appliance operation using sensor information. The front display reports status; a fault code is a starting point for qualified diagnosis.

Condensate collection

Moisture condenses as the exhaust gases cool. The condensate trap is part of the collection and drainage path; it is separate from the home's drinking-water supply.