Underfloor Heating - Use and Principle of Operation

Use

Underfloor heating is suitable for most new housing applications and in some cases refurbishments and conversions with low heat losses. It is more suited for buildings and areas of continuous or frequent use and is particularly suited for areas with high ceilings.

It is not suitable for areas that are used intermittently, have high heat losses and where large amounts of equipment or furniture are fixed to the floor. In addition underfloor heating is not suited for areas, where in the future, the location of partition walls may need to be changed.

In the case of retrofitting in existing buildings the floor construction and insulation properties may mean that the use of underfloor heating is not a viable proposition. As a result the market place for underfloor heating is mainly restricted to new builds, including extensions, where the building design can accommodate the installation requirements and reap the benefit of energy efficiency to its maximum potential.

Principle of operation

The principle of operation of the wet underfloor heating system is that heated water is circulated through an arrangement of plastic pipes which are embedded in the floor structure.

The two main types of floor structures for underfloor heating are solid floor and timber floor, each type having various construction methods depending on the overall floor make up and its designed purpose of use.

As the surface area of the floor is large compared to a radiator the floor surface temperature required to heat the room is low and close to the actual room temperature. The correct design of underfloor heating systems should be carried out in accordance with BS EN 1264: 1998 "Floor heating - Systems and components". This states that the maximum floor surface temperature should not exceed 29ºC for occupied areas, 35ºC for peripheral areas and 33ºC for bathrooms and changing areas. However, it is suggested that for areas where the occupants are in contact with the floor for long periods of time, that it does not exceed 25ºC. In the case of timber floors and other delicate floor coverings a maximum surface temperature of 27ºC is specified.

The floor surface temperature and therefore the heat produced by the system are determined by:

1. The spacing of the pipes embedded in the floor structure.

2. The thermal conductance of the floor structure and floor covering.

3. The water flow rate and water flow temperature.

The pipe spacing and proposed floor make up are fixed at the design stage, any change in the floor covering can have a dramatic affect on the performance and thermal comfort conditions produced by the system, so this needs to be carefully considered.

Control of the system once installed is therefore achieved by varying the water temperature, either by manual adjustment or automatically using weather compensation and by controlling the water flow to individual areas/circuits using room and floor thermostats in conjunction with two port valves fitted to the floor heating circuits.

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