The device and principle of operation of the storage water heater

A storage water heater, in contrast to a running water heater, constantly contains a given volume of water, which is heated and maintained within certain temperature limits. What the boiler consists of and how it provides a constant supply of hot water, we will tell you in this article.

Storage water heaters are divided according to the method of transferring thermal energy to the liquid on the model of direct or indirect heating.
The most common in everyday life are electric boilers with direct heating. Therefore, using his example, we will consider the design features of the device:

storage water heater device

External casing – prevents the destruction of thermal insulation and additionally protects the boiler from external mechanical influences.

Thermal insulation – slows down the natural cooling of water in the tank due to heat exchange with the environment.

The inner tank is a container filled with water.

The cold water pipe is the point of supply of liquid from the central or local system to the boiler.

Hot water take-off pipe – a unit for connecting a heated liquid to mixers and taps in a dwelling.

Heating element – in electric models, it is represented by a heating element.

Magnesium anode – performs the protective functions of the main elements from the destructive effects of electrochemical processes.

Thermostat – fixes and regulates the temperature of the liquid.

Control and alarm unit – allows you to regulate the amount of heating, control current processes, set operating modes.

The catalog of storage water heaters presents models of various price categories. This is due to the differences in the components and their characteristics.

In addition to protecting thermal insulation, it performs a decorative function and repeats the shape of the internal tank of a water heater. They can be made of metal or polymer materials. Structurally, they are made flat, cylindrical, rectangular (prismatic), narrow.

According to the method of fixing on the wall, there are vertical and horizontal models. The first option is more in demand due to its high energy efficiency and fast heating. The second type is relevant in rooms with low ceilings or places where the placement of a standard storage water heater is impossible. There are also universal models that can be positioned both horizontally and vertically.

Water heater Thermex N 15 U

Water heater ROYAL Clima RWH-ST30-FS

[storage, universal installation, 30 l, stainless steel, 2 kW, heating time – 78 min, 75 °, 43.5 cm x 58 cm x 25 cm]
9,099 *
6In stores: September 28 (Tue)
Thermal insulation
It is carried out with a layer of foamed polyurethane or foam rubber filling the space between the body and the tank. The substance is distinguished by a large number of air inclusions.

The larger the layer of thermal insulation, the longer the transfer of thermal energy from the coolant to the environment takes place. Thermal insulation of 3 cm or more is considered sufficient thickness. The heated water maintains the preset thermal values ​​for a long time, reducing the need to turn on the heating element again.

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It is intended for filling with heated liquid, therefore it must be sure to ensure proper strength and tightness. A tank that cannot withstand water pressure can crack and fail prematurely.

At the heart of the tank, a welded steel structure is used, which is coated from the inside with an anti-corrosion compound:

Polymer composite materials.
Depending on the model of the storage water heater, the volume of the tank varies from 10 to 200 liters. Sizes are selected in accordance with the number of people using hot water and water intake points.

Number of people consuming hot water

The number of people consuming hot water one after another

Some manufacturers make the tank completely out of stainless steel. Such tanks are protected from corrosion, resistant to aggressive substances until the protective layer is broken.

Cold and hot water pipes
Water from the system is supplied through a special pipe leading to the bottom of the tank. Additionally, the cold water pipe is limited by a divider – a barrier that prevents mixing of heated and cold liquid.


The hot water extraction tube is led to the upper part of the tank, where the hottest layer accumulates.

If the outlet hose is unscrewed in a connected storage water heater, no liquid will flow out. The maximum will pour out 0.3–0.5 liters from the top layer, and everything below the level will remain in the tank.

The situation is the same if you unscrew only the cold water supply hose. A closed outlet will not replace water with air, and the movement of the liquid will be weak or will not start at all. An additional obstacle on the way of draining water from the tank is a non-return valve.

Heating elements consist of a filament in a ceramic or quartz filler and electrical leads. The ohmic resistance of the filament determines the power of the heater. Some types of boilers can be equipped with several heating elements to increase productivity and save energy. Structurally, all electric heating elements are divided into wet and dry.

Wet ones are immersed directly in heated water. They are cheaper, but in the event of a breakdown of the insulation between the thread and the tube, all the water is energized. And whoever uses water can get an electric shock.

Heating element AC Electric WH-A6-1500

For water heaters: Electrolux / Zanussi
1,250 *
In stores: the day after tomorrow
Dry heating elements are closed with a steatite or ceramic casing, inside which there is a heating element, separated from the dielectric bulb by an air gap. In more expensive models, the gap is filled with oil, which has higher thermal conductivity and more energy efficiency.

Presented as a magnesium tube in the center of the water heater tank. It is a more active element than copper covering teng. Therefore, silicon oxide precipitates precisely on the magnesium anode, increasing the service life of the heating element.

Magnesium anode AC Electric AH-R1

For water heaters with anode hole M4i
In storage water heaters with a wet heating element and a stainless steel tank, it participates in the electrolytic process. Iron and copper are a galvanic pair and, in the presence of a weak aqueous electrolyte, enter into an electrochemical reaction. The magnesium of the anode takes a blow and breaks down on its own, preserving the basic elements of the boiler.

Measures the current temperature of the water. In case of heating up to the set limit, for example, 75 ° C, disconnects the power circuit. Storage water heaters can use mechanical or electronic thermostats.

storage water heater thermostat

The mechanical one controls the temperature by means of a bimetallic plate, which deforms from heat and moves the contacts. Electronic models are equipped with a thermistor that changes its ohmic resistance in proportion to the degree of heating.

Control block
It is represented by a push-button or sensor module at the bottom of the storage water heater. The thermometer can be performed using a dial gauge or on an electronic display. Allows you to set the maximum heating temperature, switch operating modes.

Modern models may include remote control via a mobile app. Some are equipped with hourly programming for a day or a week.

Operating principle
A boiler installed and correctly connected to the water supply system works according to the following principle:

Hot water opens and liquid is taken from the upper layers of the tank.
scheme of supply and withdrawal of water from a storage water heater

The pressure in the tank decreases until there is less pressure from the cold water pipe.

The non-return valve opens, which prevents water from returning from the storage water heater back to the system, and ensures the supply of a new portion of liquid from the pipeline.

The divider installed above the cold water inlet prevents mixing with the already heated liquid. The cold stream fills the lower volume, keeping the upper layer warm.

When there is sufficient filling with cold water, the immersion temperature sensor cools down and closes the contacts of the power supply circuit of the heating element.

Teng, located at the bottom of the tank, heats up cold water. Due to convection, the warm liquid rises upward, making room for the cold flow.

When the tank is full, the water pressure will restore and close the non-return valve.

The water will gradually heat up to the set temperature. Upon reaching this mark, the thermostat will give a signal to turn off the heating element.

operating principle of a storage water heater

The storage water heater will remain in this state until hot water is reused or until the liquid in the tank cools naturally. Due to the thermal insulation of the boiler, natural cooling takes several hours.

Summing up
The storage water heater is perfect for both apartments and private houses and summer cottages. A properly selected model can provide the whole family with hot water for many years.

The weak point of any boiler is the heating element, which suffers from limescale deposits. Hard water can destroy the heating element in a few years. Therefore, all storage water heaters are recommended to carry out periodic maintenance with the replacement of the magnesium anode.