If you are considering heat pump heating, whilst selecting the right heat pump, you will also need to decide how to distribute the heat it generates to the rooms. Underfloor heating, radiators and fan coils can all be connected to a heat pump, but they offer very different levels of comfort and possibilities.
Heat-pump underfloor heating one of its greatest advantages is that it is capable of heating even at low water temperatures a suitably sized building. This is well suited to the operation of heat pumps, as the smaller the temperature difference the system has to generate, the more efficiently it can operate. However, this does not mean that underfloor heating is automatically the best choice for every building.
A house currently undergoing renovation for example, the existing Converting a radiator system can be simpler and more cost-effective, rather than removing the entire floor. And if we also want to use the heat pump for active cooling in the summer, the fan coil or a properly designed ceiling cooling system introduces further considerations into the decision-making process. It is therefore advisable to treat the heat pump and the heat dissipation system as a single system right from the design stage.
Why do heat pumps and underfloor heating work particularly well together?
The heat pump One of the most important features of its operation is that the lower the flow temperature required, the more efficiently it can heat to heat the building. Consequently, the same heat pump may operate with a more favourable COP at a flow temperature of, for example, 35 °C than at 55 °C.
As a rule of thumb, it can be said that A water temperature that is 10°C higher can increase the electricity consumption required to generate a given amount of heat by approximately 15–25%, although the exact difference depends heavily on the type of heat pump and the operating conditions. Therefore, for any specific system, one should always refer to the manufacturer’s performance data.
For the various heat sinks, a good starting point might be, for example:
- approximately 35 °C for underfloor heating
- around 45 °C for a conventional fan coil unit
- in a radiator system, approximately 55 °C
Take the flow water temperature into account, depending on the system design.
The benefits of underfloor heating just the vast heat-dissipating surface. Whilst a radiator has to meet the room’s entire heating requirement from a relatively small surface area, with underfloor heating almost the entire floor acts as a heat emitter. For this reason, adequate output can be achieved even at lower water temperatures.
Technical literature also emphasises the importance of operating the heat pump at a low flow temperature: the correct sizing of the heat-dissipating system is therefore one of the fundamental prerequisites for the efficiency of the entire heat pump system.
Underfloor heating with a heat pump: why is this combination so popular?
Underfloor heating with a heat pump first and foremost for newly built or fully refurbished detached houses an obvious choice. It can operate at a low flow temperature whilst distributing heat evenly across a large surface area.
Underfloor heating it also feels comfortable: the heat is not emitted intensely from individual points, but from a single large surface. A properly designed system can ensure a consistent temperature throughout the room, and there are no radiators to take up space on the walls. This can be particularly important in modern detached houses designed with large glass surfaces and minimalist interiors.
Underfloor heating at the same time there are limitations. Due to the high mass of the floor structure, the system has significant inertia, and therefore responds more slowly to changes in heat demand, such as a fan coil. Both the floor covering and the entire floor structure must be adapted to the underfloor heating system.
When carrying out renovation work, the available headroom is particularly important. Installing a conventional underfloor heating system can result in a thicker floor structure; therefore, if there is insufficient structural space available, the system may reduce the headroom.
Designing heat pump underfloor heating
When designing underfloor heating for a heat pump, always It begins with determining the building’s heating requirements. There can be a huge difference in the heating energy requirements between two buildings of the same floor area. Factors that matter include the thermal insulation of the walls and floor slabs, the quality and size of the windows and doors, the building’s orientation, airtightness, ceiling height and the size of the glazed areas. It is advisable to determine heat loss on a room-by-room basis.
The output of the underfloor heating must also be calculated
The next question is whether the available floor area is capable of delivering the amount of heat required by the room in question at the desired low water temperature. The thermal resistance of the flooring, the floor’s layer structure and the furniture layout can both affect heat dissipation.
The pipe layout and the length of the heating circuits must also be calculated. The heating requirements of a living room with a large glass frontage and a small interior room may differ, so their designs may also vary.
In addition to all this, hydraulic balancing must not be overlooked. The aim is to ensure that the designed flow rate is achieved in every circuit and that every room receives the required heating output.
The cladding matters too
Ceramic and stone floor coverings are generally well suited for use with underfloor heating, as they possess favourable thermal conductivity properties. Laminate, vinyl or wooden flooring may also be used, provided that the manufacturer certifies them as suitable for underfloor heating and the thermal resistance of the entire layer structure is adequate. The choice of flooring can therefore also influence the water temperature at which the system needs to be operated.
A heat pump with a radiator: can it work properly?
Yes. It is not essential to install underfloor heating for a heat pump heating system. A well-functioning system can also be created using appropriately sized radiators. The problem usually arises when we wish to use a radiator system – originally designed for a boiler operating at a higher water temperature – with a heat pump without making any changes. As the average water temperature in the radiators decreases, so does the heating output they can provide.
That is why Before carrying out a heat pump retrofit, it is necessary to assess whether the individual radiators are capable of meeting the heating requirements of the rooms at the planned flow temperature. That may well be the case. If, for example, the building has undergone energy-efficiency improvements in the meantime, heat loss may have been reduced, and the heating system may even have become oversized in relation to the new heating requirements.
In other cases, radiators with a larger heat-dissipating surface area may be required. For more details on this, see the „What sort of radiators are suitable for heat pumps?” as we explain in our article entitled ….
A radiator-based solution can be particularly appealing during refurbishment, as it may require significantly less structural work than the retrofitting of underfloor heating.
Fan coil with heat pump: heating and cooling with a single heat exchanger
The third common solution is the fan coil, which a heat sink consisting of a heat exchanger and a fan. During heating, hot water flows through the heat exchanger, whilst the fan blows the air from the room through it. Thanks to the fan-assisted circulation, it is capable of delivering high output even at relatively low water temperatures. In heat pump systems, this can therefore offer a good compromise between underfloor heating and traditional radiators.
One of the biggest advantages of a fan coil unit becomes apparent in the summer: Active cooling can also be implemented using the same system, provided the heat pump is suitable for this. In this case, moisture condenses on the cold heat exchanger, so a condensate drain must also be fitted to the unit.
The fan coil at the same time uses a fan, so how it works not entirely silent, and it also creates air movement. In terms of comfort, it therefore offers a different experience to a surface-mounted heat dissipation system.
What happens if we also want to use the heat pump for cooling?
Radiator
A conventional radiator is not suitable for room cooling; a separate cooling solution is required in addition to the radiator system.
Ceiling cooling: a comfortable alternative
If we know at the design stage that we wish to use a heat pump for cooling, it is worth exploring the possibility of ceiling cooling. The large active ceiling surface is capable of cooling the room without draughts or fan noise; however, it is important to monitor humidity levels and regulate the water temperature.
Active cooling is easier to achieve with a fan coil unit
In the case of fan coils, the unit is designed to provide both cooling and heating, so if it is essential to use a single unit for both heating and cooling, a fan coil may be a practical choice.
Comfort: radiator, underfloor heating or fan coil?
The perception of comfort is subjective, primarily the method, intensity and noise level of heat dissipation These are the factors that determine which solution is ideal for whom.
Many people like the direct, immediately noticeable warmth of radiator heating, and a well-sized system can be very comfortable.
Underfloor heating it transfers heat over a large surface area, which is why ensures a consistent sense of warmth. The floor surface is pleasantly warm, and there are no fans or strong draughts.
The fan-coil unit circulates the air using its fan. Modern units may be quiet on a low fan setting, but they are not completely silent and do not eliminate draughts entirely. In a bedroom or any room where complete silence is a priority, it is worth taking this into account at the design stage.
How much space does each system take up?
The radiator and the wall-mounted fan coil unit remain visible features of the room. Both take up wall space, so they must be taken into account when arranging furniture and planning the interior design. From this point of view, underfloor heating is virtually invisible. There are no wall-mounted radiators, so the interior can be arranged more freely.
However, this comes at an architectural cost: underfloor heating requires a specific layer configuration. In new builds, this can be planned for from the outset; in renovations, however, the raised floor level may pose a problem or reduce the available headroom.
There are differences in maintenance too
The heat-emitting side of a conventional radiator and underfloor heating during normal operation does not require a regular annual service maintenance, like a fan-driven unit. This, of course, means that The entire heating system and the heat pump require periodic inspection.
In the case of fan coils However, it is worth to allow for annual maintenance. The cleanliness of the filters, fan, heat exchanger and – in cooling mode – the condensate drain is equally important for hygienic and reliable operation.
How much will it cost to set up the three systems?
When comparing investment costs, one must be particularly cautious when using simple prices per square metre or per unit. The final cost depends on the building’s specifications, the required capacity, the pipework, the control systems, the installation conditions and the quality of the equipment selected.
As an example of order-of-magnitude design, a complete Installation of a radiator heat dissipation point approximately 300,000 Ft each, a fan-coil unit approximately 500,000 HUF each incurs a cost, whereas underfloor heating when designing it, approximately 15,000 Ft/m² These figures are given as a rough guide. They are indicative, project-specific amounts and do not represent generally applicable market prices.
In the case of underfloor heating, it is particularly important to clarify exactly what is included in the price per square metre. During renovation, demolition, sub-floor preparation, insulation, screeding, tiling and levelling can significantly increase the total cost of the project. For this very reason, it is worth calculating the investment costs and expected running costs of a complete, fully functional system.
Is a buffer tank required?
The issue of the buffer tank depends on the heat pump manufacturer’s specifications, the system’s water volume, the minimum required flow rate, zone control and the hydraulic design.
Radiator and fan coil units, with a small water capacity or divided into many zones In such systems, a suitably sized buffer or hydraulic solution is typically required, which ensures the water volume and flow rate required by the heat pump, and reduces the risk of it switching on and off too frequently.
For underfloor heating owing to the large water volume in the pipe network and the structure’s significant heat-storing mass A separate buffer tank is not usually required.
Underfloor heating, radiators and fan coils – what are their respective capabilities?
| Criterion | Underfloor heating | Radiator | Fan coil |
|---|---|---|---|
| Typical design progression | approx. 35 °C | approx. 55 °C* | approx. 45 °C* |
| In terms of heat pump efficiency | Particularly favourable | It depends on the dimensions | It could be beneficial |
| Heating comfort | Very good, consistent | It’s very good; you can feel it more quickly | Right, but it involves air movement |
| Active cooling | To a limited extent | No | Yes |
| Fan noise | None | None | There is |
| Air movement | Minimum | Natural convection | Fan-cooled |
| Space requirements | In the floor construction sequence | On a wall surface | On a wall or ceiling |
| Reaction time | Slow | Medium | Fast |
| Regular maintenance of heat sinks | Not typical | Not typical | Recommended annually |
| Buffer tank | In many cases, this can be omitted | It is often necessary | It is often necessary |
| When renovating | Major surgery | It’s usually simpler | Moderate intervention |
*The actual design water temperature depends on the sizing of the heat emitter, the building’s heat demand and the specific system configuration.
Which heat sink should you choose for a new build?
With a new family home, we are in the favourable position of being able to coordinate the heat pump, heat emitters, cooling, ventilation and building structures right from the start. If we want an efficient heating system, underfloor heating with a heat pump is a very good starting point. It operates at a low water temperature, ensures a high level of comfort and does not take up any wall space.
However, if cooling during the summer is also important, it is worth giving this further consideration as early as the design stage. In such cases, underfloor heating can, for example, be combined with ceiling cooling fitted with humidity and dew point control. In other cases, fan coils can provide both heating and cooling.
To choose the right solution, it is worth gaining a comprehensive understanding of, What types of heating systems are available for a detached house?, and not to base a decision on just one mechanical component.
Underfloor heating isn’t necessarily the best option when renovating
When modernising an existing detached house, the optimal decision may be quite different. If the flooring is being completely replaced anyway and the building is undergoing energy efficiency upgrades, it is worth considering the installation of underfloor heating. However, if you have a radiator system in good condition, it is often more cost-effective to assess what low flow temperature can be achieved with appropriately sized radiators.
We could also consider a mixed system
It is not necessary to use the same type of heating system throughout the whole house. For example, it is possible to install underfloor heating on the ground floor, whilst fan coils or suitably sized radiators could be fitted in certain rooms on the upper floors.
The advantage of a mixed system is that heat output can be adjusted to suit the requirements of individual rooms. The downside is that Different heat sinks may require different water temperatures, flow rates and control systems, so hydraulic design is becoming more complex.
It is a particularly important principle that the efficiency of the entire system is also influenced by the highest required flow temperature. For example, it would be pointless for underfloor heating to be able to operate at 35 °C if, within the same system, a 55 °C flow temperature has to be generated due to an undersized radiator. This must be taken into account at the design stage.
5 common mistakes when designing heat pump underfloor heating systems
- The heat pump is selected based solely on the floor area. There can be a huge difference between the heating requirements of a 150 m², modern, well-insulated house and a family home of the same size that is several decades old. The basis for sizing the system is therefore the building’s calculated heat loss.
- They are designing the system with an unnecessarily high flow temperature. The system may still heat the building in this way, but in doing so we risk losing one of the heat pump’s most important advantages: its high efficiency.
- They do not take the floor covering and the layer sequence into account. When it comes to heat transfer through the floor, the thermal resistance of the materials above the pipework is of paramount importance.
- The heat pump and the heat dissipation system are designed separately. The heat pump’s capacity, the flow temperature, the heat transfer surface area, the flow rate and the control system must be determined in coordination with one another.
- They only think about the heating. In new-build projects, it is therefore advisable to clarify requirements regarding summer comfort as early as the initial mechanical engineering design stage.
Frequently asked questions about heat pump underfloor heating
At what temperature does underfloor heating with a heat pump operate?
A common design value is around 35 °C, but there is no single ideal water temperature that applies to all buildings. The required value is determined by a combination of the building’s heat loss, the design of the underfloor heating system, the outdoor temperature and the desired indoor temperature. Furthermore, with weather-compensated control, the flow temperature varies in line with the outdoor temperature.
Does a heat pump work with a radiator?
Yes. However, radiators must be sized for the water temperature at which the heat pump is designed to operate. An existing radiator may not provide sufficient heat output even at a lower flow temperature.
Is a heat pump more efficient with a fan coil than with a radiator?
In many cases, yes, because fan-assisted heat dissipation means that adequate performance can be achieved even at lower water temperatures. However, the exact difference always depends on the specific units and operating temperatures.
Do you need a buffer tank for heat-pump underfloor heating?
Not necessarily. A properly designed underfloor heating system with a large water volume can operate without a buffer tank when used with certain heat pumps. The use of a buffer tank is more commonly justified in radiator and fan-coil systems, but the final design must always be determined on the basis of the specific technical requirements of the system in question.
Underfloor heating with a heat pump or radiators? We’ll make the decision based on the entire system
If we consider only the energy efficiency of the heat pump, underfloor heating is an excellent choice: due to its large heat-dissipating surface area, it can operate at a low flow temperature. This is particularly in newly built, well-insulated detached houses makes an attractive solutionetc.
The radiator system However, this does not rule out the use of a heat pump at all. With appropriate sizing, in particular It can be a cost-effective and comfortable alternative when renovating.
Fan coils are the preferred option when a rapid response and summer cooling are both important requirements; however, one must take into account the noise from the fan, the airflow and the annual maintenance.
The best solution is always the system that has been designed to meet the specific building’s heating requirements, its use and the owner’s expectations regarding comfort.
For this very reason, when installing a heat pump, the heat dissipation system must be taken into account either before or in parallel with the selection of the appropriate unit. In a well-designed system, the heat pump, underfloor heating, radiators or fan coils, the hydraulics and the control system are all components that determine how the system as a whole operates.
If you are planning to install a heat pump heating system or modernise an existing one, it is worth thinking in terms of the system as a whole right from the start. SMARTAIR’s experts will help you design a solution that makes the most of the heat pump’s potential, taking into account the building’s characteristics, the required heating and cooling capacity, and your usage requirements.