What is underfloor heating?

Underfloor heating is a heating system in which the floor itself gives off the heat. Usually warm water flows through a network of pipes spread evenly in the floor. Electric underfloor heating uses heating cables or mats instead. Because the heat is emitted over a large area, a low water temperature is enough. That makes underfloor heating a good match for a heat pump or another low-temperature system.

Systems

• Wet system: the pipes are laid on insulation or on a structural floor and embedded in a sand-cement or anhydrite screed. This is the usual method in new build.
• Dry system: the pipes lie in grooved insulation or aluminium plates, covered with dry floor boards. Lighter and quicker, suitable for timber floors and renovation.
• Milling in: grooves are milled into an existing screed, the pipes are laid in them and finished over. The screed must be thick and strong enough for this.

Pipes are laid in a spiral (snail) or serpentine pattern and fixed with tacker clips, castellated panels or a mesh. Near external walls a smaller pipe spacing is often chosen.

Advantages and disadvantages

Advantages: even warmth, no radiators in the way, low water temperature and therefore a good combination with sustainable heat sources.

Disadvantages: the system responds slowly, so quick heating up or night setback works less well. Floor coverings affect the heat output, and retrofitting costs floor height or milling work.

Tips

• Surface temperature: the European standard EN 1264 uses a limit of about 29 °C in occupied areas, higher in perimeter zones and bathrooms. A warmer floor feels unpleasant and dries out.
• Floor finish: choose a finish with low thermal resistance. A maximum of 0.15 m²K/W is often used. Stone and tiles conduct well; thick carpet and underlay hold the heat back.
• Heating-up protocol: a new screed is heated up only after curing and step by step according to a fixed schedule. Heating too quickly causes cracks.
• Insulation under the pipes: without insulation, a lot of heat is lost downwards into the crawl space.
• Circuits and manifold: one or more circuits per room, each with its own control on the manifold, so you can balance each room.
• Drilling into the floor: before the pipes are covered, record the pipe layout with photos and a drawing.

Related terms

• Low-temperature heating
• Screed
• Anhydrite floor
• Central heating radiator
• Floor panel
• Floor tile

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