13) The Basics

The ground floor in many buildings is made up of a large slab of concrete or is constructed with concrete beams and block infill. Wet underfloor heating systems effectively use this floor area as a radiator. The surface temperature required to produce a comfortable temperature in this application is much lower than with a radiator system, and the heat is produced where it is most needed.

Insulation is put down on the concrete – usually 75mm for basements and ground floors and 25mm in heated areas in floors above. The pipe is then clipped to the insulation and connected to the manifold. When the pipe has been laid, the system is pressure tested, usually to 3 bar, which is twice the normal working pressure. On large commercial and residential projects, we issue a test certificate for each manifold that we install.

Screed is then laid; this can be either a standard 4:1 sand/cement screed with a fibre additive (75mm depth recommended) or a liquid screed (55mm recommended depth). It is very important for us to know the type of screed to be used prior to installation because the taping of the insulation differs according to the screed being used.

Time control is also important, because one of the shortcomings of the 1960’s electric systems was that, to use cheap electricity, the floor slab was heated between midnight and early morning. This produced floors that were too hot first thing in the morning and too cold in the evening when people wanted to sit down and relax.

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