Why do you need an expansion tank in the boiler

The volume of liquid substances increases when heated. Since water is an incompressible liquid, even slight heating leads to an increase in pressure in a sealed heating system.

To compensate for the excess coolant in the heat supply network, expansion tanks are mounted. They perform the following functions:

  • removal of excess water during heating;
  • liquid return to the circuit during cooling;
  • maintaining a stable pressure in the heating network by adjusting the volume of the coolant;
  • protection of all elements of the heating system from hydraulic shocks;
  • accumulation and removal of air vapors that appear when the water coolant is heated.

reference! Water contains dissolved gases, which, when heated, take the form of bubbles, enter the closed heating circuit, causing the formation of air s.

What is it needed for

The volume of a kilogram of water at 20C is 1.002 dm 3 (l), when heated to 90C it increases by 3.4% and reaches 1.036 l.

When circulating 200 liters of liquid, the difference can be 6.8 liters. For a closed heating network, this is a considerable amount and it will not be possible to distribute it through the pipes.

To solve the problem, an expansion tank is installed, a special tank connected by one outlet to the system.

During heating, the pressure inside the circuit is compensated by the volume of the tank: excess water is sent to it, and when cooled, it rushes back to the system.

Where to install an expansion tank in a closed heating system with a pump: methods and tips

Installation of the expansion tank of the heating system guarantees its full functionality and safety. Devices of such variants are used in open or closed concepts. When you decide to install the device, then you should take into account its design features, in addition, the practicality of installation.

Location of the expansion tank in the heating main https://ogon.guru

Why do you need an expansion tank in the heating system and installation features

An integral part of the heating system is an expansion tank. It allows you to control the correctness of the entire heating system. Before installing the heating unit, it is necessary to study the options offered on the market, calculate the system in relation to your own home. The way the system is installed is also important. Having previously studied the topic of interest, it will be easier to navigate what the specialist of the company where the system is purchased from offers, and it will also be possible to control the work of installers and understand what they are talking about during the installation process.

Pressure in the heating system

Before filling with water, the pressure in the pipes is 1 atm. When the coolant is poured, this indicator immediately changes, even if the liquid is still cold. The reason for this is the different arrangement of the elements of the system: with an increase in height by 1 m, 0.1 atm is added. This effect is called static. They are guided by it when designing networks with natural circulation of the coolant. One of the main advantages of this system is that pressure fluctuations can be quickly stabilized if they occur.

In a closed system, excess pressure is formed, which occurs during heating and expansion of the coolant in the pipes. It can change in different sections of the highway, so it is important to provide for stabilizing devices even at the stage of project development. Otherwise, the risk that the system fails.

Note that there is no strictly fixed pressure level for autonomous heating systems. It is calculated individually, based on the technical characteristics of the equipment, the number of storeys of the house and other factors. As a rule, the numbers range from 1.5 to 2.5 atm.

Expansion tank selection

You should think about the option of a heating system even at the stage of building a house. When all construction work is completed, pipes for water supply and heating systems are laid. The installed system means that the user knows exactly how much liquid is required to fill the hydraulic system. A boiler is purchased that meets the parameters of the area. Do not forget about acquiring an important element of the system. an expansion tank. If you want the heating system to function for more than one year and there are no various kinds of accidents, a reservoir for draining excess liquid is installed without fail.

When do you need an Expansion Tank?

  • the volume of the expansion tank must be greater than the volume of water heated to high temperatures;
  • fasteners must be of high quality, we look at the shape, the type of connection;
  • read carefully the instructions on how to install correctly;
  • we study the technical documentation before installation.

There is a huge variety of expansion tanks of different shapes and manufacturers on the market. As practice shows, you should not save on this device. It is better to choose high-quality products and from a reliable, time-tested supplier. With proper installation and operation, regular inspection, the equipment will serve for many years.

Before switching on for the first time, it is necessary to set the pressure in the air section of the diaphragm tank. It must be equal to the constant value of the pressure of the water column in the heating circuit. The necessary adjustment is done with a simple pump for machines and the control is carried out by a measuring device. a pressure gauge.

Do I need an expansion tank for a Baxi wall-mounted gas boiler?

The volume of the built-in expansion tank of the Baxi boiler is indicated in the specifications and for the ECOFOUR series it is 6 liters, in order to answer the question of its need in a single heating system. you need to know the total volume of this system.

It is not so difficult to calculate it: the filling volume of the boiler and radiators is in their characteristics, and the filling volume of pipelines can be calculated knowing their diameter and total length. Water, after heating by 80 degrees Celsius, will increase in volume by about 4-5%, therefore, the recommended volume of the expansion tank is 8% of the total volume of the heating system if filled with water and 12% if antifreeze is used as a coolant (thermal coefficient antifreeze extensions more). Thus, a regular expansion tank will be sufficient for a heating system with a volume of up to about 75 liters when using water and up to 50 liters when using antifreeze liquid.

These figures are conditional (with a margin) and when selecting the capacity of the expansion tank, you must be guided by the design calculations of a particular heating system, or the manufacturer’s recommendations.

In most cases, the built-in boiler tank is sufficient and the decision to use a separate additional tank is made by specialists at the design stage.

How to make your own hands from plastic containers or stainless steel

Expansion tank can be made independently. A tank of 1012 liters is suitable for this (depending on the exact calculations of the volume of the coolant of the general system).

What does an expansion tank do?

If you have a ready-made base, for example, a plastic container, you should check its capacity (with ordinary 3-liter jars), and then fix the missing elements.

Usually the tank is made of stainless steel sheet 24 mm thick.

  • welding machine, electrodes for welding;
  • angle grinder with matching wheels;
  • sheet metal (stainless steel);
  • nozzles;
  • various bolts, a set of fittings;
  • rubber pads;
  • brush, gloves, protective mask;
  • Oil paint;
  • thermal insulation materials;
  • file for metal;
  • roulette;
  • tank diagram with all dimensions.
need, expansion, tank, boiler

Metal sheet marking

First of all, you need to make a markup on sheet metal. To do this, you can use the cutting map with paper parts, allowing you to use the metal with the least waste. When joining two parts on a sheet, it is imperative to take into account the thickness of the angle grinder circle, which can eat several millimeters.

Important! All work should be carried out carefully, followed by cleaning the edges.

Cutting blanks

The tank body consists of five or six rectangles (depending on the presence of a cover). If desired, you can divide the upper part of the cover into two parts as it will be convenient, by welding one part to the base, and attaching the second to the curtains.

Welding a homemade device

Cut blanks must be placed at a right angle and welded. The method of fastening can be different gas is perfect for 2 mm steel sheets, and with 34 mm sheets it is good to work with electric welding.

It is necessary to make a hole in the bottom of the housing and weld a pipe there, through which the coolant will enter the tank. Connect the pipe itself, respectively, to the circuit of the general heating system.


The open heating structure is distinguished by the installation of an expansion tank at the highest point of the system. Usually, this is an unheated attic, where the temperature is often below zero in winter. Under such conditions, the water in the tank can freeze, damaging the entire system. To avoid such a problem, the tank should be insulated with special materials, for example, basalt wool.

Such a heat-insulating material is resistant to high temperatures, which is a necessary condition, t. To. water in the tank, at elevated degrees, boils.

Adding oil

In the design of a homemade tank, in addition to the main pipe connecting the tank to the system, additional elements are welded:

need, expansion, tank, boiler

Important! The drain pipe must be located above the limit fill level of the tank in order to avoid liquid overflowing over the top.

Through the hole in the lid, water from the tank evaporates and air can enter the system. This leads to overheating of the pipes and poor circulation of the coolant. To solve this problem, professionals recommend pouring a little oil into the tank. It will tighten the surface of the coolant with a thin film, thus creating a protective layer against air penetration.

How to calculate tank volume

When calculating the volume of the expansion tank, several factors must be taken into account:

To calculate the capacity of the tank, the formula is used:

Vb tank capacity;

Vc is the volume of coolant in the system;

K liquid expansion coefficient. For water, this figure is 4%, so 1.04 is used in the formula;

D expansion coefficient of the tank itself, depends on the material of manufacture and the temperature difference during heating. To accurately establish D, you can use the formula:

D \u003d (Pmax Pini) / (Pmax 1), where:

Pmax is the value of the maximum pressure inside pipes and radiators;

Pnach is the pressure inside the tank, planned by the manufacturers (usually 1.5 atm.).

Thus, the volume of the tank depends largely on its own characteristics.

Attention! All indicators and characteristics should not exceed the established standards. When calculating the volume of the device, the data must be equal to or slightly larger than the results obtained.

Many sites offer online calculations for expansion tanks.

How the boiler expansion tank works

Expansion tank selection

Choosing an expansion tank for heating is a responsible matter. In this case, it is necessary to pay attention not only to its type and size, but also to the membrane. such indicators are important: resistance to the diffusion process, operating temperature range, durability, compliance with sanitary requirements.

In addition, it is necessary to determine the ratio of the boundaries of the pressure range, which is the maximum allowable. Be sure to check before buying a tank whether it meets existing quality and safety standards.

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