What is the difference between a single-pipe and a two-pipe heater?
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Stefano Fonseca ist Ingenieur für Energie und Umwelt mit über sechs Jahren Erfahrung in der technischen Gebäudeausrüstung (TGA). Er kombiniert technisches Fachwissen mit einer Leidenschaft für verständliche Kommunikation. Seit mehr als fünf Jahren schreibt er als freiberuflicher Redakteur über erneuerbare Energien und nachhaltiges Wohnen, insbesondere über Photovoltaik und Wärmepumpen.
In many older buildings, there is a heating system behind the walls that hardly anyone is familiar with — and yet has major effects on efficiency and modernization. Single-pipe or two-pipe heating: The difference is invisible but decisive. Anyone who wants to convert, renovate or switch to a heat pump should know him in detail.
What is a single-pipe heater?
The single-pipe heating system is an older heating system in which all radiators are connected in series. The heating water flows through each individual radiator one after the other and gradually releases heat. It is only at the end of the line that it returns to the boiler.
With single-pipe heating, only a single pipe runs through the room or floor. Each radiator is connected to this pipe. The heating water flows through the first radiator, loses temperature and then reaches the next one. To allow a certain degree of controllability, a so-called bypass line with a valve is often used. This ensures that some of the heating water can flow past the radiator.
Single-pipe systems were used primarily in the 1950s to 1980s. They are often found in post-war apartment buildings and in multi-storey residential buildings. This system is also widely used in prefabricated buildings in the GDR.
A hydraulic balancing Is particularly complex in single-pipe systems. Since all radiators flow through one after the other, each one influences the pressure and temperature in the entire string. Radiators usually get more heat at the beginning than those at the end. Without precise adjustment of the bypass valves and flow rates, uniform operation is hardly possible. Automatic hydraulic balancing can help, but is technically more complex than with two-pipe systems.
What is a two-pipe heating system?
Two-pipe heating is a common heating system in which all radiators are connected to two pipes in parallel. A flow pipe supplies each radiator directly with heating water at the same temperature, while the return pipe brings the cooled water back to the heat source.
In a two-pipe system, there are two separate lines: the flow and the return flow. Each radiator is connected independently to both lines. This means that all radiators receive water at almost the same temperature at the same time. After the heat has been released, the water is returned to the boiler or heat pump via the return line.
The two-pipe system allows significantly better heat distribution, as no radiator is dependent on the upstream temperature of other radiators. Each room can be controlled independently, which increases comfort and saves energy. It is also possible to use modern thermostatic valves.
The two-pipe heating system is ideal for use with a heat pump. Since heat pumps operate with low flow temperatures, uniform heat distribution is crucial for efficiency. Hydraulic balancing is also relatively easy to implement.
What is the difference between a single-pipe and a two-pipe heater?
Two-pipe heating is now the standard and meets modern requirements significantly better. It enables efficient heat distribution, precise regulation and is ideal for operation with heat pumps. Single-pipe heating, on the other hand, is considered obsolete and can only be brought up to today's energy standards with great effort.
You can find an overview of the differences in the following table:
Can a single-pipe heating system be operated with a heat pump?
Only under certain conditions and with technical adjustments. This is because single-pipe systems rely on high flow temperatures, as the heating water flows through several radiators one after the other. However, heat pumps work efficiently at low temperatures. This often results in uneven heat distribution and limited controllability.
Automatic hydraulic balancing can optimize flows and make the system fit for heat pump operation. If such an adjustment is not possible or not sufficient, the only alternative is the conversion to a two-pipe system or the use of panel heating systems.
Convert single-pipe heating to two-pipe heating
A conversion from a single-pipe to a two-pipe heating system can be worthwhile if the existing system is inefficient or needs to be converted to a heat pump. Although expenditure is high, heating costs fall and living comfort increases significantly in the long term.
New supply and return pipes must be installed for the conversion. Existing radiators can often be reused as long as they are suitable for low-temperature operation. The heating control must be adjusted and a hydraulic balance must be carried out. In Apartment Buildings, the Procedure may be more extensive if several strands are affected.
The following is an overview of the costs - these are only indicative values for single-family homes (without wall or floor openings):
About the program “Heating optimization” The BAFA Are individual measures eligible for funding — in particular hydraulic balancing and the installation of modern components. Die Funding amount is 15%, with Another 5% bonus When incorporating an individual restructuring schedule (ISfP).
Single-pipe heating or two-pipe heating — which is better?
Two-pipe heating is much better suited to today's requirements and is therefore the preferred solution. It enables uniform heat distribution, precise regulation of every radiator and is ideal for operation with heat pumps. In contrast, single-pipe heating is considered obsolete, difficult to control and only partially efficient. Anyone who wants to modernize or switch to renewable heating technology should therefore opt for a two-pipe system in the long term.
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