An underfloor heating system is designed to compensate for heat losses through walls, doors, windows and roofs. This heat loss is greater in areas that experience lower outside temperatures. For each home, the heat output, in W/m2, that is required to overcome those losses and provide a comfortable room temperature, is calculated based on data specific to the home design and location.
A system design also needs to consider the type of flooring to be used, as this too impacts on the required heat output. Each type of flooring has a different thermal resistance, known as an R value (or alternatively TOG = 10 x R value). The higher the R value, the higher the required heat output. Any floor finish on top of an underfloor heating system must not exceed an R value of 0.15.
|Thermal Resistance |
|Typical example of floor finish|
||2mm vinyl tile, 5mm ceramic tile, 3mm epoxy coating|
|0.05 m²K/W||25mm marble floor|
|0.10 m²K/W||9mm carpet floor tile, 13mm hardwood|
|0.15 m²K/W||Deep pile carpet, wood blocks, 22mm laminates|
Each system is designed for a room temperature of about 20°C for the occupied areas, or 24°C in bathrooms and similar areas. The floor surface temperature to achieve this varies for each home, but never exceeds 29°C in occupied areas except for bathrooms (max. 33°C) and peripheral areas (max. 35°C) i.e. hallways etc that contain connecting pipes.
The heat output of the system is controlled by three different parameters:
The higher the temperature of the water in the underfloor heating circuits, the higher the floor heat output. The water temperature is adjusted at the manifold mixing valve.
The higher the flow rate of the water in the underfloor heating circuits, the higher the floor heat output. The flow rate for each individual circuit is adjusted at the corresponding flow meter on the manifold.
The smaller the distance between the pipes within the concrete, the higher the floor heat output. Most installations will have 200mm pipe centres which gives a good temperature distribution, although in some specific cases where for some reason a lower heat output is required, 300mm centres may be used.