Heat pump with radiators?
Works (almost) always!

There is a persistent myth that you have to operate a heat pump with underfloor heating or other panel heating in existing buildings. In this article, we explain why, in the majority of cases, you can keep your old radiators.

Status: 09.04.2024

How can you operate your new heat pump in the most energy-efficient way possible?

The structural condition of your old building is crucial for low flow temperatures - and therefore the lowest possible power requirement for your heat pump. All measures that prevent heat from escaping from the building to the outside also increase the efficiency of your heat pump, as you can run it at a lower heating output. Energy-efficient renovation and modernization in old buildings include new windows or retrofitting insulation to the roof, facade and basement ceilings. Of course, it can also make sense to replace existing radiators, so seek advice from an experienced heating engineer. The correct dimensioning of the heat pump is also extremely important. A dimensioning according to the motto "A lot of kW heating capacity helps a lot" unnecessarily drives up the costs of purchase and operation. We recommend our specially trained heating engineers in the alpha innotec specialist partner network. After refurbishing your heating system, they will also carry out the necessary hydraulic balancing professionally.

Good to know: As a general rule, your heat pump will always work particularly efficiently if the heating system operates with a low flow temperature. The flow temperature in itself depends on the size of the surfaces available for heat transfer and the heat demand in your home.

The difference between radiant and convection heat

The heat from your heating system is essentially transferred into the room in two ways. In the first case, known as convection heat, the air flowing past the radiator or panel heater is heated. The air expands and rises towards the ceiling. Colder air flows in from the floor. This permanent heat flow gradually distributes the heat throughout the room.

Radiant heat, on the other hand, is generated when the heating energy from the radiator or panel heater is transferred directly to solid objects such as walls, objects, people or animals via electromagnetic waves. These heat up and in turn transfer the heat to the room.

The balance between radiant and convection heat varies from heating system to heating system. As a general rule, conventional radiators heat with up to 90 percent convection heat. With modern ceiling heating, it is pretty much the other way around. Studies show that we find radiant heat more pleasant and warmer than convection heat. That's why you can usually set the room temperature around 2 degrees lower with panel heating without compromising on comfort. This alone saves you 6 percent energy per degree. That should not be underestimated!

Radiant heat versus convection heat

Radiant heat versus convection heat

Which radiator types are suitable for operation with a heat pump?

Good to know: Underfloor heating systems have larger surfaces for heat transfer, which means that the flow temperature required to heat the rooms is correspondingly lower. This makes underfloor heating systems, as well as wall and ceiling heating systems, ideal for the efficient operation of a heat pump. In combination with a powerful heat pump, however, you can usually also keep your conventional panel radiators.

In a finned radiator or sectional radiator , steel or cast iron sections are arranged in a row through which the heating water flows. This original form of radiator can often be found in unrenovated old buildings. They mainly transfer heat via convection. To generate a comfortable room temperature, they require high flow temperatures due to their small surface area and are generally not suitable for operation with heat pumps. Like sectional radiators, tubular radiators also consist of individual elements. They are often installed as towel radiators in new buildings.

Panel radiators can be found in most existing buildings. They consist of several hollow bodies arranged one behind the other, through which the heating water flows. Convection plates in between increase the heating surfaces. Panel radiators emit a large proportion of the heat energy via radiation. For this reason, they are suitable for operation with a heat pump in many cases, provided they are sized accordingly.

Heat pump radiators or low-temperature radiators are a special type of panel radiator. Small fans inside them increase convection, so they can be operated at lower flow temperatures with the same size.

Funktionsprinzip Fußbodenheizung

Functional principle of underfloor heating

1) Warmes Wasser strömt durch Rohre im Fußboden und beheizt dessen Oberfläche. An der warmen Oberfläche erwärmt sich die Luft.
2) Die warme Luft steigt auf, überträgt ihre Wärme auf die kühleren Oberflächen und sinkt wieder zu Boden: Die Luft zirkuliert im Raum.
3) Auch der Fußboden sendet Wärmestrahlung aus. Wegen der starken Konvektion bleiben die Oberflächen aber trotzdem immer kälter als die Luft.

Schon die alten Römer wussten die Vorteile von Fußbodenheizungen zu schätzen. Das Heizwasser fließt durch im Boden verlegte, dünne Rohre aus Kunststoff oder Kupfer. Da die Wärmeübertragung über eine große Fläche erfolgt, können sie mit einer niedrigen Vorlauftemperatur betrieben werden. Für die nachträgliche Installation einer Fußbodenheizung gibt es spezielle Dünnschichtsysteme mit niedriger Aufbauhöhe. Bei Fußbodenheizungen ist der Anteil der Konvektionswärme noch sehr hoch – im Gegensatz zur Wandheizung und vor allem zur Deckenheizung, auch als Klimadecke bekannt. Wie die meisten Fußbodenheizungen eignen sich Wand- und Deckenheizungen in Kombination mit einer Wärmepumpe für die Klimatisierung. Übrigens ist auch das Nachrüsten von Wand- und Deckenheizungen im Altbau meist kein Problem. Sie sind als Komplettpaket mit Dämmung erhältlich und erhöhen signifikant die Effizienz deiner Wärmepumpe.

Funktionsprinzip Deckenheizung

Functional principle ceiling heating

1) Warm water flows through pipes in the floor and heats its surface. The air heats up on the warm surface.
2) The warm air rises, transfers its heat to the cooler surfaces and sinks back to the floor: The air circulates in the room.
3) The floor also emits heat radiation. However, due to the strong convection, the surfaces always remain colder than the air.

Good to know: Do you want to find out whether you can operate your existing radiators with a heat pump? Lower the flow temperature to 50 degrees Celsius on a very cold day. If the heating output is sufficient, talk to your heating engineer about installing a heat pump without replacing the radiators or get advice on how you can replace them with efficient radiators or a panel heating system as cheaply as possible.

Which heat pump can be operated with conventional radiators?

Radiators can be operated with both ground source heat pumps and powerful air/water heat pumps. Heat pumps with the refrigerant propane (R290) are particularly recommended for renovating heating systems in old buildings. Thanks to the excellent thermodynamic properties of the refrigerant, our Hybrox 11/16 air/water heat pumps, for example, can achieve flow temperatures well above 70°C. Even at -22°C and a flow temperature of 65°C, you don't need to switch on a heating element and can keep practically any old building warm in winter. Also make sure that your heat pump works with modern inverter technology. As the heat pump system adapts its output continuously and flexibly to demand, it works at the optimum operating point and only ever produces as much heat as is needed.

The Fraunhofer study will convince you

The efficiency of heat pumps is often discussed, but the fact that they are usually much more energy-efficient than gas heating, even in older buildings, and in any case more climate-friendly is often not mentioned - especially in combination with photovoltaics. Just ask yourself whether there is any reason to burn oil or gas at 1,000 degrees to heat your living room to a cozy 21 degrees. Instead, heat pumps use heat from the ambient air, the ground or groundwater. Find out more about this ingenious operating principle here.

Last but not least, back to the topic of flow temperatures. In old buildings, this does not always have to be above 70 degrees, as is often feared. In a field study by the Freiburg-based Fraunhofer ISE, which was also supported by the ait Group, the maximum flow temperatures required for heating in existing buildings averaged just under 44 degrees Celsius. So your chances are good that you can retrofit a heat pump with existing radiators.

Wärmepumpe LWD Neubau

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