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Heat pumps without underfloor heating: a useful option?

A heat pump in combination with an area heating system is considered the ideal setup and is standard in new builds. However, many renovators are confused about whether a heat pump is also an option in buildings without underfloor heating. The answer is yes, especially if a few points are observed. Read on to find out what those are and how you can increase heat pump efficiency in existing buildings without underfloor heating.

Low flow temperatures enable high efficiency

In homes with conventional heat pumps, environmental energy can be harnessed to heat the central heating water. This then flows to the heating surfaces in the house to release thermal energy into the rooms. It doesn't matter whether this involves an area heating system such as underfloor heating or radiators for the heat pump. However, the type of heating surface is important when it comes to energy efficiency. This can be understood by considering how environmental heating works.

Technical process raises the temperature level of the environmental energy

Whether a heat pump is used in combination with underfloor heating has no influence on its mode of operation. The underlying technical process is always the same.  

Low flow temperature improves efficiency

The temperature of the heat source (air, ground) and the heating water flow temperature determine how efficiently a heat pump works without underfloor heating. The smaller the difference between these temperatures, the less power the compressor requires (see step 2 in the previous section). With lower power consumption, the seasonal performance factor increases and heating bills come down.  

Heat pumps also suitable for existing buildings without underfloor heating 

Flow temperature is important for heating system efficiency and depends not only on the type of heating surfaces, but also their properties. For example, some radiators can transfer sufficient heat to surrounding rooms with low heating water temperatures. Here's an overview: 

  • Panel radiators: Panel radiators such as the Vitoset universal radiators from Viessmann consist of flat or profiled panels with convection plates between them. As heating water flows through the heating plates, they give off heat to the room and the air in it. If you have panel radiators and would like to retrofit a heat pump without installing underfloor heating, this can generally be achieved. However, the heating surfaces should be as large as possible.
  • Low temperature radiators: Low temperature radiators are panel radiators characterised by a special flow pattern and large transfer surfaces. They achieve high performance values even at low flow temperatures and are therefore also suitable as radiators for heat pumps.
  • Heat pump radiators: Heat pump radiators are another type of panel radiator. However, they are equipped with small fans that ensure a higher air flow through the heating plates. This increases performance and enables the heat pumps to be operated without underfloor heating at lower flow temperatures. 

While these panel radiators are suitable for heat pumps, the same cannot generally be said of old cast iron and sectional radiators. Just like designer and tubular radiators, these have a small transfer surface, which necessitates high flow temperatures. 

Area heating systems help lower heating costs

From a technical perspective, there is no requirement for underfloor heating when operating a heat pump. When it comes to the level of heating costs, however, the combination is advantageous. This is because area heating systems manage with low flow temperatures thanks to large heat transfer surfaces. These ensure that heat pumps with underfloor heating alone are usually more energy efficient. Large panel, low temperature and heat pump radiators achieve the same result and also help ensure that environmental heating systems operate economically.

Increase the efficiency of radiator systems and save on heating costs  

When optimising an existing heating network, you can reduce your bills with a heat pump, even in existing buildings without underfloor heating. Measures that lead to a reduced flow temperature are important here. We have five tips to share.

The heating curve assigns a specific flow temperature to each outside temperature. Once optimally adjusted, this is quite sufficient to compensate for heat losses via the building envelope and achieve the required room temperatures. An incorrectly set curve results in excessively high flow temperatures and this is reflected in your heating bills. A contractor can help you find the right setting.

Heating water always follows the path of least resistance as it passes through a heating system. If this is the same for all heating surfaces, there are no problems and all rooms get the heat they need. If it is not, however, then some rooms get too much heat while others remain cool. Higher flow temperatures provide a remedy, but result in increased heating costs. Heating system installers use hydronic balancing to optimise systems and thus also help to save costs when installing a heat pump without underfloor heating.

If you operate a heat pump without underfloor heating, even individual radiators can impair energy efficiency. Identifying and replacing these can lower the flow temperature and save energy. Energy consultants and contractors are there to help with this.

If you have all these tips covered and would like to save even more, you can combine an environmental heating system with a solar installation, namely a solar thermal or photovoltaic system. While the former contributes free heat to the heating system, the latter covers part of the power demand. In both cases, your consumption of electrical energy is reduced and you save costs with the heat pump, even in existing buildings without underfloor heating.  

In addition to building services measures, you can also increase the thermal insulation. New windows and doors as well as ceiling, wall and floor insulation lower heat demand. The flow temperature can be reduced and the efficiency of the heating system increases.

Utilising subsidies for radiators and heat pumps together

Thanks to state subsidies, you can save costs when installing a heat pump in an existing building, even without underfloor heating. Opt for an air source heat pump, for example, and you become eligible for attractive subsidies. What many people don't realise is that these also cover all environmental measures. If you are planning hydronic balancing, having the heating curve adjusted or replacing radiators, you can also include the costs incurred for this when applying for a heat pump subsidy. The same holds if you are retrofitting an underfloor heating system.

Tip: If the costs exceed the subsidy budget, you can take a step-by-step approach. First apply for a subsidy for the heating system optimisation and only then for the subsidy for the heat pump without underfloor heating.

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