How to select and connect the storage boiler indirect heating

A smart choice for securing a consistent supply of hot water in your house is the installation and selection of an indirect heating storage boiler. The efficiency and compatibility of this kind of system with your current heating system are well known. For best results and energy savings, it’s important to know how to select and connect this kind of boiler, whether you’re building a new house or replacing your old hot water system.

It’s crucial to comprehend what an indirect heating storage boiler is and how it operates before making a purchase. Indirect systems use the primary heating system in your house to heat the water, which is then stored in a tank. This is in contrast to direct heating boilers, which produce heat directly within the water. Because it frequently makes use of the excess heat from a boiler or furnace that would otherwise be wasted, this technique has the potential to be more energy-efficient.

A number of considerations need to be made when selecting a boiler, such as size, compatibility with your current heating system, and insulation qualities. Your household’s water demand should determine the boiler’s size. An overly large boiler can result in energy waste, while a boiler that is too small won’t be able to meet your daily needs. In order to get the best results, the boiler and your current heating system must be compatible. This brings us to another important point.

After selection comes installation, which usually calls for expert assistance because of how intricately it must be integrated with the central heating system. In addition to guaranteeing effective operation, proper installation increases the boiler’s lifespan. It’s critical to collaborate with a trained specialist who can make the required modifications to your central heating system and guarantee that everything is connected securely and correctly.

All things considered, an indirect heating storage boiler can provide dependable and effective hot water, making it a wonderful asset to your house. With careful model selection and installation, you can have hot water whenever you need it for comfort and convenience without having to pay a lot of money for energy.

2 types of tank heaters for DHW

A domestic indirect heating boiler is a 50–300 liter metal tank that prepares hot water using an external heat source, such as a boiler, furnace with a water circuit, solar collector, or, less frequently, a geothermal installation (heat pump). Water-heating devices are classified into two types based on the device and its working principle:

1. The most common variant – with a heat exchanger in the form of a coil made of copper or stainless steel.
2. Tank-in-tank" design, where the heating element is an internal stainless steel tank.

The accumulation tank is shaped like a cylinder or in another way, but it always has rounded ends. A welded rectangular tank (from the English tank) won’t last long because the water pressure frequently reaches 6–8 bar; the flat walls will bend and the tank will burst at the seams.

Reference: As seen in the picture below, certain two-circuit gas boiler models have indirect heating tanks housed inside the heat generator. The integrated storage tanks have a maximum capacity of 80 liters.

We will provide a thorough explanation of each kind of indirect boiler to help you make an informed decision and make sense of the situation.

Appliances with spiral heat exchanger

The components of this type of tank boiler are as follows:

• indirect heating tank is made of stainless steel or black metal covered with heat-resistant enamel;
• metal tank is equipped with spigots for connection to the water supply network and immersion sleeves for the installation of thermostats or temperature sensors;
• inside the tank is installed heating element – spiral coil, connected to the heating system of a private house;
• to protect the steel vessel from the effects of electrochemical corrosion is used magnesium or titanium anode, which gradually deteriorates during operation;
• outside the tank is insulated with 30-50 mm thick polyurethane foam, the front lining is thin sheet painted metal or polypropylene casing;
• the front part of the unit is equipped with a scale of an arrow thermometer.

Note: Manufacturers occasionally include a spigot with an automated air vent, drain cock, and other practical features with their products.

The boiler works on a very basic principle: coolant that has been heated to between 70 and 90 degrees Celsius is fed into the coil through the upper pipe, rapidly heating the entire volume of water in the tank. Via the bottom pipe, the cooled coolant is redirected back into the boiler.

The top section of the tank is used to extract hot water, while the bottom is used to replenish it. The thermostat and three-way valve, which are a part of the boiler piping scheme that we will examine later, regulate loading (heating) to the desired temperature.

Details for contrasting. When heated to 45 degrees, the water heat exchanger (indirect) can produce power ranging from 12 kW (80 liters in the tank) to 25 kW (200 liters). The boiler water temperature ranges from 80 to 90 °C. One kW heating elements are used in electric boilers. 2.5 kW out of 5. According to information from the French manufacturer Atlantic, the minimum and maximum heating times for 100 liters of water are 25 and 150 minutes, respectively.

We have looked at a reasonably priced single-circuit water heater model. What other kinds of devices are available on the market?

• boiler with two heat exchangers for connecting an additional heat source;
• Combined storage tank with a heating element for direct water heating, schematically shown in the sketch;
• vertical models in floor and wall-mounted versions;
• wall-mounted boilers of various shapes – round horizontal, narrow elongated (Slim), flat double-chamber boilers;
• universal storages fixed to the wall in any position – horizontal or vertical.

Important point. Boilers that are wall-mounted have connections at the bottom, and a tube for hot water intake from the upper layers is located inside the tank. The tube from the cold water supply connection is lowered to the bottom of the tank in floor models, and the appliance’s side or top have the connection threads. Watch the video to learn how the water heater operates.

Tank-in-tank construction

The boiler’s exterior is identical to that of its "counterpart," with a cylindrical insulated body, spigots for connecting sanitary and heat-carrying water, and a thermometer scale. The water heater has a distinct internal layout:

1. The outer tank, made of ordinary carbon steel, serves as a water jacket for the inner tank. The coolant heated to 80-90 °C circulates between the walls of the two vessels.
2. The inner cylindrical tank is welded from stainless steel.
3. Inside the heated tank there is a temperature sensor sleeve and a water inlet/outlet pipe (depending on the orientation of the body in space). No magnesium anode.
4. The useful capacity of the DHW circuit is approximately 70% of the total volume of the boiler.
5. Thermal power of 100-liter apparatus reaches 18 kW with heating surface area 1.03 m², full load time – 10 minutes (data from Belgian manufacturer ACV).
6. The heated boiler is able to function in flowing mode – the heat exchange area is enough to produce hot water "on the run". One condition: the boiler equipment must ensure the required flow rate of the coolant. For example, a 100 liter model (DHW tank is 70 liters) may request 1.5…2.5 tons of heating medium per hour.

The vessel is depicted in section in the diagram below, and it is easy to see how the tank walls’ wavy profile was created for these purposes:

• the corrugated structure of the side walls allows the vessel to expand / contract when heating / cooling water;
• Increased heat exchange area;
• the mobility of the corrugated profile provokes self-cleaning of internal surfaces from limescale.

A combined version of "tank-in-tank" water heaters with direct heating elements is also offered. When the boiler’s contents reach a predetermined temperature, the tubular element turns on automatically. It also functions in the summer when the heating system is turned off. An electronic control unit is used by the user to set the temperature.

To be clear. The boiler coolant, not the sanitary water within the stainless tank, is heated by the heating element in contrast to electric boilers.

Indirect water heaters with two walls are more robust and efficient; manufacturers guarantee a five to ten-year service life. Another benefit is easier maintenance; the user doesn’t have to worry about replacing the magnesium anode every two years or check its condition. Now for the drawbacks:

• heating jacket takes away 25-30% of the useful volume of the tank, traditional coil – up to 10%;
• models equipped with an electric heating element cannot be mounted horizontally;
• the unit can only be transported in an upright position.

Note: The "cold" branch pipe of a boiler destined for horizontal installation is fixed to the wall with its downward orientation.

The reasonable price of water heaters is one of their main drawbacks. Let’s compare two similar-quality units: the 300-liter ACV SMART LINE E 300 and the 300-liter DRAZICE OKC 300 NTRR. The price of a boiler with a coil, called "Dražice," is 750 u. е., and a Belgian ACV "tank within a tank" heater is 1720 u. е. The cost of the Czech model with two heat exchangers is twice that of the single-circuit "Belgian" model.

Selecting an indirect boiler

Learn the following details to select the ideal indirect heating tank for your home or apartment:

1. Number of permanently living people and water consumption mode. The aim is to calculate the total flow rate of sanitary hot water.
2. Water heater capacity is limited by the capacity of the boiler and solar collector. If the heat source has not yet been installed, select heating equipment with a capacity reserve of 50-100% for the boiler load.
3. Allocate space for the appliance and think about the method of installation – wall or floor mounted.
4. Decide on the functionality of the heater – whether you need a heating element or a second heat exchanger.

A small detail to consider when placing the storage tank is that there is an expansion tank next to the boiler, with a volume equal to 10% of the main reservoir’s capacity. A boiler room is the ideal space to put in a country cottage.

We suggest using the minimum indicators to determine how much water the DHW system uses. A single person requires 32 liters of warm water in a single day—20 liters for bathing (showering) and another 12 liters for household necessities. A family of two, then. For three people, you will need a boiler that has a minimum capacity of 100 liters and a useful volume of 50 to 80 liters. Select a tank with a capacity of at least 120 liters if you intend to fill the bathtub. The table below displays an abridged version of the selection algorithm:

The heat generator’s power has a significant impact on how quickly the tank heats up. It is useless to install a 200-liter storage tank if the building is heated by a 10-15 kW boiler because the house will have time to cool down while the water is heated. The important thing to remember is that heating is not as important as boiler loading. Put simply: the radiator network won’t get the necessary amount of heat until the drum reaches the necessary temperature.

This is an illustration of how to calculate boiler capacity:

1. Initial data: the volume of the boiler is 200 liters, the temperature in the HTW system – plus 10 ° C, DHW – 50 degrees Celsius.
2. To heat 1 kg of water by 1 degree it takes 1.16 W of heat energy. Calculate the heat consumption for 1 hour: 1.16 x 200 x (50 – 10) = 9.28 kW.
3. To reduce the loading time fourfold (up to 15 min), it is necessary to supply 4 times more energy – 9.28 х 4 = 37.12 kW. Result: the power of the heating unit in maximum mode is 40 kW, otherwise the boiler will take longer to heat up.

Overall suggestions for selecting an "indirect heater":

• if the budget allows, it is better to buy a heater of the "tank-in-tank" type – the device is more efficient in operation, maintenance – only annual flushing;
• always check the useful capacity of the tank – it is 10-30% less than the declared dimensions due to the volume occupied by the heat exchanger;
• it is better to take a large-capacity accumulator in the floor version;
• A horizontal boiler suspended closer to the ceiling is suitable for apartment buildings;
• in the absence of solar collectors, it is worth paying attention to combined models that ensure the operation of DHW during the warm period;
• The minimum wall thickness of the enameled tank should be 2 mm.

Note: The weight of the working tank can be used to estimate how thick its metal walls are. Fine 80-liter boiler, 2 mm metal construction, "tightens" approximately 25 kg.

Iron tanks are much less expensive than stainless steel but are virtually just as reliable due to their covering of heat-resistant plastic enamel enhanced with zirconium. Welded seams, which effectively corrode in the event that the magnesium anode is completely exhausted, are the weak point of stainless steel. It is recommended to select a product with a titanium electrode as it has a three-fold longer lifespan.

Homeowners should match the boiler’s capacity to the hot water demands of their household and make sure it works with their current heating system when choosing and installing an indirect heating storage boiler. Selecting a boiler that can meet peak hot water demands without wasting energy requires a certain amount of volume. In order to maximize efficiency and reduce heat loss, proper installation involves connecting the boiler to the central heating system and calls for careful attention to detail regarding pipework and insulation. Choosing a boiler with a high energy efficiency rating and adequate insulation can drastically improve the overall heating performance of your home and save operating expenses.

Bundling of the "indirect boiler" with the boiler

Installing the unit on the floor or firmly attaching it to a concrete or brick wall is the first step. Avoid wall mounting if the partition wall is composed of porous materials (aerated concrete, foam block). Maintaining boiler maintenance requires a 50 cm clearance when installing on the floor from the closest structure.

Important: Carefully read the instructions before attempting to fix the boiler’s wall-mounted horizontal model. The cold water spigot is typically located at the bottom of the device when it is hung. It is not acceptable for the coil and the heating element to be in the upper zone if the tank is upside down.

The following scheme is used to connect a boiler to a gas or solid fuel boiler that isn’t fitted with an electronic control unit.

Let us enumerate the primary components of the boiler circuit and denote their respective purposes:

• automatic air vent is placed at the top of the supply line and is engaged in the discharge of air bubbles accumulating in the pipeline;
• circulation pump provides the flow of coolant through the loading circuit and coil;
• Thermostat with immersion sensor stops the pump when the set temperature inside the tank is reached;
• The check valve eliminates the occurrence of parasitic flow from the main line to the boiler heat exchanger;
• the diagram does not conventionally show cut-off cocks with American style valves, designed for disconnection and maintenance of the device.

Note: A 25-40 pump will work fine for the loading circuit’s typical operation (pressure head: 0.4 Bar). There is little difference in installing the element on the supply or return line. The pumping unit is located on the supply side of the tank in the plumbing layout depicted in the installation handbook for DRAZICE water heaters.

In a similar vein, larger, intricate systems featuring multiple boilers and heating circuits are linked to the heater. The sole requirement is that the boiler be connected to the mains first so that it can receive the hottest coolant. The hydrostrelka’s distribution comb is connected directly to the boiler, bypassing the three-way valve. An illustration of the primary/secondary ring piping scheme is provided.

The manufacturer advises using an expansion tank and a safety group connected to the coolant outlet when connecting the boiler "tank in a tank." Justification: there is nowhere for the liquid to go when the internal DHW tank expands and the water jacket volume drops. The applied fixtures and equipment are depicted in the figure.

Wall-mounted boilers with a specific connection fitting are the easiest to connect to an indirect heating boiler. Through a three-way switching valve with an electric actuator that is managed by the boiler controller, other heat generators that are outfitted with electronics are connected to the water heater. The following is the algorithm:

1. When the temperature in the tank decreases, the thermostat signals the boiler control unit.
2. The controller gives a command to the three-way valve, which transfers the entire heating medium to the DHW tank load. Circulation through the coil is provided by the built-in boiler pump.
3. When the set temperature is reached, the electronics receives a signal from the boiler temperature sensor and switches the three-way valve to the initial position. The heat transfer medium flows back into the heating network.

Vital. When connecting a two-circuit gas boiler to the storage tank, the aforementioned plan is also employed. Connecting the "indirect boiler" to the heat generator’s DHW line is not acceptable.

The following diagram illustrates how the solar collector is connected to the second boiler coil. The heliosystem has its own expansion tank, pump, and safety group, making it a fully functional closed circuit. In this case, a separate unit is required to regulate the manifold’s operation in response to signals from two temperature sensors.

Video: the simplest scheme of connection of a wall-mounted boiler

Connection on the water supply side

The connection is made using the standard plan depicted below if the water intake points are situated close to the heating tank. Let’s go over each element’s purpose:

• A pressure reducer is recommended for pressure surges above 6 bar;
• A check valve on the HTW supply prevents the tank from emptying into the water main;
• The expansion tank compensates for the increase in the volume of the heated liquid;
• safety valve, set to 7 bar, discharges water into the sewer in case of pressure rise to a critical point;
• The drain cock is used to drain water by the method of communicating vessels.

Take note! Use an expansion tank intended for higher pressure applications, such as 6 or 8 bar systems, in water supply systems. Heating the tank will quickly render the membrane useless, so it is not recommended.

In situations where customers live far from the boiler, installing a recirculation line with a backup pump and check valve makes sense. Just tap the return line into the cold water inlet line if your heater model does not have a separate connection for this line.

It is necessary to fill the internal tank of a system with a tank-in-tank heater with sanitary water before pumping the coolant and doing pressure testing. The master will go over the specifics in the video:

Electrical connection diagram

When connecting the combined tank with TEN to the home power grid, keep in mind that the main coil will stop receiving heat from the boiler when the system enters summer mode. We recommend using a universal scheme that includes a thermostat-controlled pump control module.

In the event that the sanitary water temperature rises, a second safety thermostat in the system is triggered. Lamp: an indicator that lets you know when the heating element is on.

The effectiveness and comfort of your home heating system can be considerably improved by selecting the appropriate storage boiler with indirect heating. To make sure the boiler satisfies your needs without wasting energy, it’s critical to take your household’s water usage into account when choosing the boiler’s size and capacity. To optimize efficiency and minimize installation difficulties, the type of boiler you choose should also work with the heating system you currently have, whether it is an oil, gas, or solar configuration.

Seeking professional assistance during storage boiler installation is imperative for both safety and optimal system performance. A professional will connect the boiler to the heating system in your house and make sure that all of the parts, including the pumps and heat exchanger, are installed and operating correctly. This meticulous attention to detail increases the boiler’s lifespan and helps to avoid future maintenance problems.

Maintaining the proper operation of your storage boiler requires routine maintenance. Annual check-ups can help identify problems before they become more serious and require expensive repairs. This entails monitoring the pressure levels, looking for leaks in the pipes and connections, and making sure there is no build-up of limescale in the heat exchanger, which can have a negative effect on efficiency.

To sum up, installing and choosing a storage boiler with indirect heating for your house is a wise investment. Proper size, compatibility, expert installation, and routine maintenance are key components of a dependable and effective heating system that offers warm, comfortable water all year round. Making a wise choice now can result in lower long-term costs and more comfortable living spaces.

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