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Underfloor Heating

Underfloor heating uses the floor surface itself as a heat emitter. For wet system the heat is supplied by appropriately spaced pipes embedded beneath the floor surface, usually within the screed of a solid floor.

Floor heating has very different heat emission characteristics from radiator heating. Floor surface temperature is critical to comfort, as well as to heat output. The option floor temperature range for comfort lies between 19 and 26°C, so systems are normally designed to operate at no higher than 26°C in living areas. Higher temperatures are acceptable in bathrooms and close to external walls with higher heat loss, such as beneath full-length windows.

The design surface temperature is controlled by the spacing between pipes and the flow water temperature. It is also affected by floor construction, floor covering and the depth of the pipes beneath the floor surface; detailed design procedure are given by system manufactures. In practice, systems are usually designed to operate at flow temperatures of between 40 and 60°C, with a temperature drop of between 5 and 10° C across the system. Maximum heat output is limited to the maximum acceptable surface temperature; between 50 and 100 W/m² is typical in living areas. The maximum rate of heat emission available is 11 W/m² per degree of temperature difference between floor and air temperature in the room.
The overall design of underfloor heating systems should be undertaken in accordance with the Standard BSEN 1264-3; 1997. Parts 1, 2 and 3.

Underfloor heating may be used in conjunction with radiators, for example for the ground floor of a house with radiators or the second floor. Separate circuits are required in such cases, typically using a mixing valve to control the temperature of the underfloor circuit.

Underfloor heating is best suited to well insulated houses, in which it can provide all the required heating load. It is also more suitable for reception rooms than for rooms requiring intermittent heating, such as bedrooms, because it has a slower thermal response than radiator systems.