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Glossary · Energy industry & energy transition

Hydraulic balancing

Hydraulic balancing Heating heat pump flow temperature return temperature Efficiency building

Hydraulic balancing refers to the professional adjustment of a water-based heating system. The aim is for every radiator and every heating circuit to receive exactly the volume flow of heating water needed to provide the required space heating. It is therefore not a blanket optimisation of the heating system, but concerns the distribution of heating water in the pipe network. In a balanced system, nearby heating surfaces with favourable flow conditions do not receive too much water, and distant or unfavourably connected heating surfaces do not receive too little.

Physical background

The decisive technical variable is the volume flow. It indicates how much heating water flows through a heating surface or a heating circuit per unit of time, for example in litres per hour. Together with the temperature difference between flow and return (the spread), it determines how much heat output is transferred. The flow temperature is the temperature of the water flowing from the heat generator to the heating surfaces. The return temperature is the temperature of the water coming back after releasing its heat. An example: if a radiator is to deliver 1 kW at a spread of 10 kelvin, it needs around 86 litres of water per hour. At a spread of 5 kelvin it would be about twice as much. Balancing brings these variables into a sensible relationship: enough flow for space heating, but no unnecessarily large water volumes, no excessive pump pressures and no artificially high system temperatures.

Without balancing, water mainly takes the path of least resistance. Radiators close to the pump or on favourable pipe sections receive more water than necessary, while those further away receive too little. In practice this is often masked: the heating curve is set higher, the circulation pump runs harder, individual thermostatic valves are opened further, and other rooms are overheated. The system then produces enough heat but distributes it poorly. The building appears heatable even though the hydraulics are not right.

Distinction from related activities

Hydraulic balancing is not merely bleeding the radiators, even though air in the system can also disrupt heat distribution. Nor is it general boiler maintenance or the replacement of thermostatic heads. Thermostatic valves control room temperature by throttling the flow at the radiator. Balancing creates the precondition for this control to work within a usable range. It is also not the same as adjusting the heating curve: the heating curve determines which flow temperature is provided at which outside temperature. Balancing ensures that this temperature is distributed in the building according to demand. In technical and legal usage, however, adjusting the flow temperature control belongs to the scope of a complete balancing. Both steps are therefore closely linked.

Procedures and components

In Germany, the industry associations' technical rule "Optimierung von Heizungsanlagen im Bestand" (optimisation of existing heating systems) distinguishes two approaches. In the simplified procedure A, the heat load is estimated using characteristic values. In the more precise procedure B, the heat load is calculated room by room, in accordance with DIN EN 12831-1 in conjunction with DIN/TS 12831-1. In addition, the heating surface outputs are checked, the resistances in the pipe network are taken into account, and the required volume flows and valve presettings are determined. For the statutory obligation and for the federal funding, procedure B or an equivalent procedure is decisive. Verified digital or adaptive procedures are also considered equivalent if they meet the requirements set for this purpose.

In underfloor heating, the individual heating circuits are adjusted at the manifold. In radiator systems, this is done via presettable thermostatic valves, lockshield (return) valves, riser balancing valves or differential pressure controllers. Modern high-efficiency pumps help with operation but do not replace a correct hydraulic design. A pump can deliver pressure, but it does not know on its own which room has which heat load. If balancing also includes checking the heating surfaces, it may turn out that individual radiators are too small. In that case no valve setting helps, only a larger heating surface.

Significance for efficiency

Balancing matters for the efficiency of a heating system because incorrect distribution is almost always met with makeshift solutions. If a room does not get warm, rarely does anyone check the volume flow first. Usually the flow temperature is raised or the pump is set higher. As a result, the energy consumption of the heat generator or the electricity consumption of the pump increases, and controllability deteriorates. Oversupplied rooms have to be throttled by the thermostatic valves, while undersupplied rooms still remain short. The system works against itself: it generates high temperatures and pressures to cover up a distribution fault.

This becomes particularly clear with the heat pump. It works more efficiently the lower the flow temperature can be. Every unnecessary temperature increase enlarges the temperature lift between the heat source and the heating system and lowers the seasonal performance factor. A poorly balanced system can therefore turn a technically good heat pump into a disappointing one. If individual rooms do not get warm because of insufficient flows, the heating curve is often raised. All rooms are then supplied at a higher temperature, although there is only a distribution problem. The fault then lies not in the heat pump alone but in the interaction of heat generator, heating surfaces, pipe network, valves and control. The law therefore expressly names checking the heating surfaces with a view to the lowest possible flow temperature as part of balancing.

Balancing also has an effect on condensing boilers. Condensing technology makes better use of the condensation heat in the flue gas when the return temperature is low enough. Excessively high return temperatures, for example due to excessive flows and too small a spread, weaken the condensing effect. A suitably set volume flow helps bring the spread and return temperature into a favourable range. How large the effect is depends strongly on the condition of the building, heating surfaces, pipe network and user behaviour. Balancing therefore does not guarantee a particular savings rate. Frequently cited flat-rate figures should not be uncritically applied to individual systems. However, balancing eliminates a common cause of unnecessarily high operating temperatures.

Legal situation in Germany

Since 1 October 2024, section 60c of the Gebäudeenergiegesetz (Building Energy Act) has required hydraulic balancing. The obligation applies to water-based heating systems when a heating system is installed or set up and put into operation in buildings with at least six dwellings or other independent units of use. The provision followed the time-limited obligation under section 3 of the Energy Security Ordinance EnSimiMaV. Unlike that obligation, it is not limited to particular fuels. In July 2026 the act was restructured into the Gebäudemodernisierungsgesetz (GModG, Building Modernisation Act). The rule on hydraulic balancing continues as section 60c, and a failure to carry out balancing, or carrying it out late, is still classed as an administrative offence.

The statutory minimum scope comprises three points: a room-by-room heat load calculation, checking and, where necessary, optimising the heating surfaces with a view to the lowest possible flow temperature, and adjusting the flow temperature control. The result must be recorded in writing, including, among other things, the setting values, the building heat load, the set output of the heat generator, the design temperature, the controller settings and the pressure in the expansion vessel. Tenants can demand this confirmation. For single- and two-family houses and smaller multi-family houses with fewer than six units, there is no general statutory obligation arising from this. For heat pumps in larger buildings, the law additionally provides its own inspection obligations during operation.

Irrespective of building size, balancing according to procedure B is a requirement under the Federal Funding for Efficient Buildings (BEG). If a water-based system is funded, it must be hydraulically balanced and the balancing must be confirmed using the prescribed form. The amount of funding and the applicable version of the guideline change repeatedly. This should be checked for currency before every application.

Common misunderstandings

  • Just a formality for funding: Funding programmes have made the term better known, but its technical meaning does not come from the form. The obligation to provide proof is meant to prevent new heat generators from being connected to poorly adjusted distribution networks. If an old boiler is replaced by a heat pump while heating surfaces, valves and pump settings remain unchanged, the new technology inherits the old faults. Efficiency problems are then attributed to the heat pump although they lie in the heat distribution.

  • All rooms equally warm: Balancing does not mean that all rooms are supposed to become equally warm. Rooms have different uses, heat loads and target temperatures. A bathroom is usually designed differently from a bedroom, and a corner room with large exterior surfaces needs more output at the same temperature than an interior room. Balancing therefore distributes not equally but according to demand.

  • Comfort problems as a control fault: Noisy radiators, overheated rooms or constantly closing thermostatic valves are often blamed on the control. The cause, however, can be excessive differential pressures or incorrect valve settings. Conversely, a balanced system can also run badly if the heating curve is set too high, the night setback is unsuitable or thermostats are used like on-off switches. Balancing does not replace good operational management.

  • Once and for all: A balancing applies to a particular system state. After insulation work, replacement of radiators, a new heat generator or a change in room use, the heat load and settings should be rechecked.

Significance for the electricity system

For the electricity system, the term is becoming indirectly more important because more and more heat is generated electrically. Heat pumps increase the electricity demand of buildings but work very efficiently when low system temperatures and stable volume flows are possible. Poor hydraulics shifts heat problems into electricity consumption: the heat pump runs at a higher temperature lift with a poorer coefficient of performance. In unfavourable cases, an electric backup heater may also step in more often. Across many buildings, this difference can become significant, especially on cold days, when heat loads and electricity demand are high anyway. Building services thus influence not only the heating costs of individual households but also load profiles, grid load and the need for flexibility.

Assessment

Hydraulic balancing shows that efficiency in buildings rarely comes from the device alone. A heat generator has a rated output and an efficiency or performance factor, while the building needs heat at particular times and temperatures. In between lies a distribution network that follows physical resistances and must be ordered by valves, pumps and control. Properly understood, hydraulic balancing is the demand-based adjustment of this heating water distribution, supported by a heat load calculation. It does not replace insulation or a good control strategy. But it helps decide whether heating surfaces, heat generator and control work together or whether efficiency is lost through incorrect distribution.

Sources

Related glossary entries

Edited by eCMS on 12.11.2026 05:10

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