how to choose a boiler module for home heating

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Selecting the correct boiler module is a key step in installing a modern heating system, as this component ensures safe operation and optimal heat transfer. An improperly dimensioned module can lead to excessive pump loading, energy losses, or even damage to the boiler itself. In this article, we will look at the technical aspects of selection so that you can choose a solution exactly according to the needs of your home.

Understanding the difference between unmixed and mixed circuits

First, it is necessary to determine the type of required circuit, which depends on whether you want to regulate the temperature in floor heating or simply distribute hot water to radiators. Unmixed circuits are intended for systems with high supply temperatures, where water from the boiler is directly fed into radiators without mixing with return water. On the contrary, mixed circuits include a three-way valve that mixes hot water from the boiler with cooler water from the return pipe, thus achieving a lower temperature suitable for floor heating.

Unmixed circuit: Ideal for older systems with radiators, where simple heat transfer is sufficient.
Mixed circuit: A necessity for floor heating, warm air heating, or combined systems.
By-pass version: Requires a separate by-pass valve in the circuit to protect against stagnation.

Dimensioning the DN diameter and pump performance

For most common family homes with a heating area up to 150 m², a standard DN 32 diameter is sufficient to handle flows up to 2.75 l/s without the risk of pipe noise. The selection of the pump must respect the total hydraulic resistance of the system, which is formed by the length of the pipe, the number of bends, and the type of valves; a too weak pump will not sufficiently force the circulation, while a too strong one will generate unnecessary noise and electricity consumption. When selecting a specific model such as Boiler Module HEAT BLOC K31 with Grundfos pump, it is critical to check the pump curve against your calculations to avoid situations where the pump operates at maximum efficiency outside its range.

The role of the by-pass valve and protection against stagnation

In unmixed systems, where a three-way valve is not built-in, it is absolutely essential to use an external by-pass valve that protects the boiler from overheating in the event that all thermostatic heads in the radiators close the water supply. Without this valve, the pressure in the system would rise sharply and the safety valve on the boiler would continuously discharge water, leading to inefficiency and the need to replenish water. For such solutions, we recommend boiler assembly with an integrated by-pass valve, which is fully prepared for immediate installation without the need to purchase additional components.

Principle of operation: The valve opens if the pressure in the system exceeds the set value (usually 0.5 to 1 bar).
Mounting position: Must be placed in parallel to the largest consumer or just before the boiler inlet.
Safety: Prevents "stagnation," which is a condition where water in the boiler does not move and quickly boils.

Choosing a pump brand: Grundfos versus DAB

The competition between the brands Grundfos and DAB in the boiler module sector is very close, as both offer reliable EVOSTA-type pumps with automatic speed regulation. The difference often lies in the details of the construction and the availability of spare parts, but for the average user, the decisive factor is the noise level and the ability to adapt to changes in the hydraulic circuit. The DAB.EVOSTA3 pump, which you will find in many of our assemblies, is known for its resistance to coarse impurities and long bearing life, while the Grundfos UPM3 Auto L stands out for its extremely quiet operation and precise electronics.

Apartment metering assemblies and their specifications

In addition to the pure boiler module, there is a category of apartment metering assemblies that serve to separate and measure heat consumption in individual apartments or zones. These assemblies often do not have their own cabinet and must be installed in a separate distribution panel or box, with the key function being the accurate measurement of flow and temperature difference. If you need to solve heat distribution for multiple zones without using complex control units, an apartment metering assembly without a cabinet represents an economically advantageous and technically functional solution for professional installers.

Without cabinet: Allows flexible integration into various types of distribution panels.
Without meter: The assembly contains only the valve, and measuring elements are purchased separately according to requirements.
KV value: Parameters KV 2.75 ensure sufficient flow for standard apartment applications.

Installation procedures and common installation errors

The most common mistake during the installation of a boiler module is the incorrect direction of water flow, which can lead to damage to the pump or malfunction of thermostatic valves. Always pay attention to the arrows on the body of the valves, which indicate the direction of flow, and thoroughly flush the pipes before starting the system to remove impurities that may have formed during installation. Another critical point is the orientation of the pump, which must always have the shaft in a horizontal position to avoid friction and premature bearing wear.

Hydraulic Separation and Mixing Valve

In multi-purpose heating systems, where the supply temperature changes depending on the season or type of zone, hydraulic separation is essential. This solution allows the boiler to operate at an optimal temperature regardless of the pressure and flow required by the heating circuit.

Frequently Asked Questions

How to determine whether you need a mixed or non-mixed setup?

You need a mixed setup if you have underfloor heating or warm air heating that requires a lower supply temperature than the boiler provides. Radiator systems are usually sufficient to be served by a non-mixed setup.

Can I use a pump from a different brand than the one included in the setup?

Technically it is possible, but not recommended, as it may void the warranty of the entire setup and you may not achieve the same energy efficiency and noise level.

Why is the three-way valve not moving in the mixed setup?

The reason may be a stuck valve due to deposits, a faulty servomotor, or an incorrectly set torque limit, which requires inspection and possibly cleaning.

Choosing the right boiler module is an investment in the long-term reliability and energy efficiency of your heating system, so it is worth spending time on technical analysis before purchasing. With our ready-made setups and expert advice, you can be sure that your system will operate smoothly even on the coldest winter days.

Do you have a question on this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.