UNDEFLOOR HEATING

When installing wood flooring over an Underfloor Heating System, installers/specifiers should consider the wide ranging temperatures which will influence movement. During the summer months the timber will expand whereas during the winter, when the heating is switched on, the timber will shrink.

Only engineered wood flooring specifically approved for use over radiant heat should be used. Installing flooring which is not approved over a radiant heat source will void any product warranty and may result in damage to the floor. It is also vital to understand that the surface temperature of the timber floor covering should not exceed 27°c (81°f); otherwise excessive gaping between boards and/or cracking of the top layer may occur. For wider hardwood boards, which are more susceptible to changes in moisture, a maximum surface temperature of between 22° - 24°c (72° - 75°f) would be appropriate.

Its is usually sufficient to provide a comfortable environment in newly built properties with adequate insulation and is generally brought about, in water feed systems, by a water circulation temperature of 35° - 45°c (95° - 113°f) or, in Electric systems, with temperatures equates to an average power output of approximately 100W/m2. It is important to note that the exact heat output will vary according to the thermal conductivity and resistance of the system and floor covering used (species, thickness etc) therefore it is important that a dedicated thermostat is installed at floor surface level to allow the temperature to be accurately controlled.

Pipes and cabling must be evenly laid out. Water pipes are usually spaced at no more than 300mm centres and Electric matting should be laid evenly, on a levelled subfloor, throughout the floor area in order to avoid local 'hotspots'. When under floor heating systems are installed at ground or basement floor level (lowest level of property), the heating elements are usually covered beneath a screed. The recommended depth of the screed may vary between 30mm and 75mm, while deeper screeds will aid in heat dissipation and will help prevent local hotspots from occurring. Allow the screed sufficient time to fully dry and ensure that the equilibrium relative humidity is certainly no more than 75%RH but ideally no greater than 65%RH.

Once the heating system is installed, and before any wood flooring is laid, the heating system should be turned on gradually in maximum 5°c (41°f) increments a day and should be run at half to two-thirds its maximum power for two weeks, followed by maximum power for 2 - 7 days prior to installation of the flooring. The room should be ventilated briefly every day during this period.

The under floor heating is generally switched off when laying the floor in order to prevent moisture being driven to the underside of the boards. Whilst this is not strictly necessary in the case of nailed or floating system, it is especially true when stick-down systems are installed. After the floor has been installed, the heating should be turned back on very gradually over a period of several days. Sudden changes in temperature such as testing period should be avoided as this can 'shock' the timber and cause rapid irreversible setting of the wood.