Underfloor heating is significantly easier and cheaper to install in a new extension at the construction stage than it is to retrofit afterwards. For any extension with a new concrete ground slab or beam-and-block floor, the question of whether to include underfloor heating should be resolved before the floor is laid.
There are two types of underfloor heating system. Wet underfloor heating circulates warm water through pipes embedded in or below the floor screed. The pipes connect to a manifold that regulates the flow from the boiler or heat pump. Electric underfloor heating uses electrical heating elements under the floor finish. Wet systems are generally more cost-effective to run and are preferred for whole-floor applications. Electric systems are simpler to install and lower in capital cost, making them suitable for smaller areas such as a bathroom or utility room.
For a rear extension with a new concrete slab, wet underfloor heating is typically the right choice. The construction sequence is straightforward: after the slab is poured and cured, the UFH pipes are laid and pressure-tested, then the screed is poured over the pipes. This sequence adds relatively little time to the programme and the additional cost of the UFH pipework, manifold, and screed over a conventional floor finish is approximately sixty to one hundred pounds per square metre of heated area. For a twelve square metre kitchen extension, this represents an additional cost of roughly seven hundred to twelve hundred pounds for the UFH system itself — a very modest premium for what becomes a permanent feature of the house.
The floor finish must be compatible with underfloor heating. Stone, porcelain tile, and engineered timber work very well. Carpet significantly reduces the heat transfer efficiency of the system and is not recommended over underfloor heating. Solid timber boards can be problematic due to thermal movement. Check the manufacturer's guidance for any specific floor finish before finalising the specification.
Underfloor heating runs at lower flow temperatures than traditional radiator systems, typically thirty to fifty degrees Celsius compared to sixty to seventy degrees Celsius for radiators. This makes it particularly compatible with heat pumps, which are most efficient at low flow temperatures. If a heat pump is being considered now or in the future, sizing the extension floor slab for underfloor heating from the outset is a straightforward way to future-proof the heating system.
The connection of the UFH manifold to the existing boiler adds five hundred to one thousand five hundred pounds depending on the distance and complexity of the pipework run. Zone control thermostats add two hundred to four hundred pounds per zone.
RCB includes underfloor heating options in our pre-construction consultation for all extension projects. 07359 872594 | contact@rcbgroup.co.uk | www.rcbgroup.co.uk