Underfloor heating

Manifold and heat sources

The basis of every underfloor heating installation is a manifold, divided into a number of circuits. Each circuit carries warm water through a loop and back to the manifold.

The heat source is not part of the installation itself. Heat sources can be: a boiler, district heating, a heat pump, or a hybrid combination. These are divided into Low Temperature (30–50 °C) and High Temperature (50–90 °C). The underfloor heating itself always operates between 28 and 35 °C — despite these low temperatures, the system provides sufficient heating capacity by making optimal use of the floor surface area.

The video shows a High Temperature heat source. Because underfloor heating operates at low temperature, the supply from an HT source is mixed with the return water from the circuits. This happens via the pump on the manifold, creating two loops: the primary line from the source to the manifold, and the underfloor heating circuits. Both circulate independently.

The number of circuits is determined by: surface area, primary or supplementary heating, insulation value, pipe diameter, whether or not a circulation pump is used, and any zone regulation.

Installation methods and patterns

The installation method varies per project and can be divided into wet build and dry build.

In wet build, a screed of sand-cement or anhydrite is poured over the underfloor heating pipes. Is there already a screed of at least 30 mm? Then milling can be used. Is there no screed yet? Then the pipes are bound to steel mesh. Where the structural floor cannot be insulated from below, tacker or stud plates provide a solution — these are installed on top of the structural floor. After installation, the screed is poured by a third party.

Dry build is the solution for structures with limited load-bearing capacity or build-up height. The floor is constructed from gypsum fibre boards such as Fermacell or Knauf Brio — no water needed. After screwing and gluing, the boards are milled for the pipes.

The spacing between the pipes determines the heating capacity. The standard spacing is 10 cm. At cold bridges such as sliding doors, the pipes are placed closer together — so-called edge zones. In rooms with less heating demand, such as the hallway or toilet, they are spaced further apart. Does a room already have another heating source? This is called supplementary heating.

The pipes are preferably laid in a spiral pattern. This provides the most even heat distribution. A meander pattern would create cold spots where the return pipe runs.