When installing underfloor heating (UFH) in your home or business property, an important factor to consider is the maximum operating temperature of the heating system under fault conditions. A typical underfloor heating system might be designed to operate at a maximum underfloor temperature of 55˚C for a screeded floor and possibly higher for a suspended or timber joisted floor. However, the control systems or the arrangement of the pipes involved in an underfloor heating (UFH) system could lead to a faulty valve or thermostat allowing water of a much higher temperature into the underfloor system. If this fault is not swiftly dealt with, the high temperature water allowed into the system can lead to damage of the underfloor heating pipe and the floor covering as well as the invalidation of the manufacturer’s or installer’s guarantee. Faults can occur with a condenser boiler despite the use of modern sophisticated controls, and modern heat pumps can also give way to high temperature flow if a component fails. However, faults most likely occur because the settings of the heat source have been altered without professional guidance.
The temperature limit of 55˚C is a limit imposed by the European Standard for UFH (underfloor heating) [BS EN 1264]. This limit is necessary as it provides a safe point over which the aforementioned damage can begin to occur to screeded floors, possibly leading to screed failure. The Domestic Building Services Compliance Guide 2010 for the Building Regulations also recommend that for any floor type, whether screeded, joisted, or other, the underfloor heating (UFH) system should be fitted with controls limiting the maximum temperature to 60˚C whether using a dry (electric) or wet (water) underfloor heating system.
Floor coverings and the Temperature limits of Underfloor Heating
Different floor coverings can handle different temperatures when used above a system of underfloor heating (UFH). Generally, the maximum temperature a floor covering can handle will vary from product to product, and the covering manufacturer should be able to provide detailed information about its product’s heat sensitivity.
However, a few temperature guidelines to follow include:
- Wet rooms not exceeding 33˚C and the perimeter zone of up to 1 metre 35˚C;
- Vinyl and Linoleum flooring not exceeding a temperature of 27˚C;
- High Duty Plastic sheeting flooring not exceeding 29˚C;
- Carpets and carpet tiles accepting any temperature within the range of the system.
Considerations for the system Designer
The task of ensuring that an underfloor heating system remains within its limit of 55˚C is allocated primarily to the system designer. The designer should therefore:
- Determine the maximum temperature that the underfloor system could potentially reach under fault conditions (for both boiler and thermostat controls), which in certain circumstances could be the maximum flow temperature that the boiler can achieve;
- Determine whether water heated to the maximum temperature could cause damage to the underfloor heating (UFH) system, the floor structure, or the floor covering;
- Consider the necessity further preventative measures, such as the use of underfloor heating pipe with a higher temperature rating and/or additional safety controls to limit the maximum possible temperature at the flow manifold;
- Decide whether floor temperature sensors, which cut off the flow of water if the temperature becomes too high, could benefit your particular system;
- Consider, in cases where the heating system will be used also as a cooling system in the summer months, the minimum temperature that the underfloor heating (UFH) system should take whilst understanding that too low a temperature can lead to condensation on the underfloor heating pipe, within the floor, and on the floor covering.