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Society / Lifestyle Choices

What is underfloor heating exactly?

Underfloor heating has been around for a long time      

Underfloor heating is a form of heating that is built into the floor. Already in Roman times underfloor heating was applied by hot air from a wood fire in a hollow space under the floor. In the system channels of about 60 cm high in the floor were built and covered the entire floor surface. That way the floor turned into a single large hot air channel. To heat spaces were the chimneys was branched out into the rooms. The fire in the space under the room heated the first floor and then subsequently the chimneys. Because hot air rises, the other rooms were heated as well, although at lower temperature. The Koreans had an even more sophisticated system in their luxurious homes in Asia. A difference with the system of the Romans is that their fireplace was in the kitchen was and that it was also used for cooking. The Romans fireplace was usually outdoors.

Today there are several systems, which can work with either an electric system or with hot water.

How does underfloor heating work?

Underfloor heating warms the floor of a room in an evenly manner through heat radiation. Because of the fact that the floor is heated with a relatively low temperature and has a smooth surface, there is hardly any convection. The heat is almost entirely spread over the entire floor by ways of radiation. The heat output is the same anywhere in the room and there is only minimal of temperature stratification in the air of the room. This creates a very comfortable temperature.

The underfloor heating system is connected to a thermostat or a weather-dependent control that regulates the temperature. By using an electronic thermostat the temperature can be programmed. Underfloor heating can replace the radiators of the central heating system if the radiating surface is sufficiently large. The heat output of the floor depends on several factors, such as temperature of the floor, the room air temperature, thickness of the floor and the type of floor. The heat output is usually between 30 and 60 W/m². Up to 100 W/m2 can be achieved.

(interior photography by Photographer Stirling)

Benefits of underfloor heating

  • Because there is a larger radiating surface with a lower temperature, it is a more pleasant heat than with radiators and the air temperature can remain relatively low. This means lower energy consumption and the House has a greater heat buffer, so that it is more regularly heated. The heat source does only need to work at lower temperatures, which is sufficient because of the higher energy output of the floor.

  • When using underfloor heating as the main heating source of the house there are no radiators and that contributes to the living space.

  • The system also gives the possibility to cool the house using a cooler or heat pump that destracts water from a deeper surface


  • A disadvantage of underfloor heating is that the pipes have to be placed in the floor. So typically this is only done in new builds or during major renovation of the property. However, it is also possible, to grind slots in the concrete subfloor, where then pipes can be placed.

  • When using carpets and other insulating floorscovers the output will be less if compared to tiles or a stone floor.

  • When the layout of a space is modified by inserting or removing walls, it is not always easy to adapt the floor underfloor heating. 

  • Any leaks in the system can only be restored by opening the floor. 

  • In case of large glass surfaces a cold draught of air can be caused because of the floor not being able to heat up the air. An additional heating suspended in the floor can overcome that problem. 

  • Underfloor heating is slow system: it heats up slow (in the winter does it take some time before the room is warm) and it slowly cools off (in the summer, this can lead to a sudden warm rooms). 

Warm water systems

With under floor heating with hot water, the pipes are generally connected to the central heating system. A manifold suitable for underfloor heating ensures that the temperature does not exceed 45° c. Underfloor heating is also widely used with low temperature heating systems such as a heat pumps. The heat pump works the most efficient at low temperatures. An underfloor heating system can then be designed is such a way that only a maximum temperature of 35 ° c is sufficient. In most occasions the warm water flows through plastic pipes with a diameter of 16 to 20 mm. These tubes are in the form of a spiral or meander, the spiral is preferred because the supply and return will always run next to each other, resulting in an even more gradual heat output. The ‘ heart on hart’-distance between the tubes is usually between 10 and 20 cm, depending on the heat requirement. The maximum length of a group lies between 70 and 120 m.

An alternative to the system with heat distribution by using a manifold is connectinf the tube to the return of a radiator. This is widely applied in areas where both are present such as bathrooms. The benefits of combined radiators and underfloor heating are warm feet and fast heat-up. The system, however, is hard to regulate, but easy to apply.

Underfloor heating with hot water can be divided into 2 groups of construction: sceeded floor systems and suspended floor systems.

Screeded floor systems

The most common form of underfloor heating is a screeded systems. This technique lays the heating pipe fully and directly in a sand-cement grout nor cast floor. The screeded system is cheaper than suspended flooring systems but has a much longer warm-up time. However it is still the most used system by Underfloor Heating Glasgow, because of a combination of the typical Scottish climate and costs. A second drawback is the drying time of the floor. This comes down to approximately 1½  centimeter per week for sand-cement floors, but less then a day for modern cast floors. A method to speed up the drying time is to use anhydrite.

Suspended and floating floor systems

Suspended floor systems come in a number of variations. Through innovation, there are currently dry building systems on the market that allow almost all kinds of floor coverings. A good example of dry building systems is the use of expanded polystyrene (styrofoam) plates with an aluminum glued lamella which allows for a good heat distribution. In this system the tube can be easily laid in the preformed cutout and fitting is therefore very fast. Such a system is much more responsive.


Underfloor heating systems can be used as a cooling method. The installation must be specifically designed for both heating and cooling. Cooling by means of underfloor heating is increasingly used as houses getting better isolated and more and larger glass area’s are used in the design. The water is usually cooled by means of a cooler or indirectly through ground water from the primary circuit of the groundsource heat pump. The energy consumption of this form of cooling is significantly lower in comparison to air conditioning.

For more information about underfloor heating systems in Glasgow Scotland, please follow the link below.