So what are the advantages over conventional systems? For starters, there are no ugly radiators hogging wall space. Convector radiators, found in most central heating systems, shoot the hot air straight up to the ceiling where it circulates downwards as it cools: the air current picks up dust at floor level and distributes it all over the furnishings. Underfloor systems work particularly well with condensing boilers, as the water return temperature is below 50°C, enabling the boiler to operate at its maximum efficiency.
Both concrete and suspended timber floors can be used with underfloor heating. With concrete, a layer of insulation is laid, followed by plastic piping to carry the warm water. This is buried in concrete with the whole slab acting as a heat store.
Suspended timber floors require the installation of special aluminium plates laid over the joists. The heating pipes lie in recesses in the plate, heating the whole plate. Conventional sheet material or floorboards are laid on top. Underfloor heating systems run at about 28°C, making them suitable for use with all types of floorcoverings including carpets.
Underfloor heating can be run in conjunction with conventional radiators, but requires a dedicated circuit because of the lower temperatures involved. A "mixing set" takes the return water from the underfloor side of the system and mixes it with the hot water from the boiler to achieve the correct flow temperature. An alternative is to use a heat exchanger between the two types of system to transfer heat while keeping the heating water isolated.
The system can be controlled conventionally using a wall-mounted thermostat, although Chris Twinn of consultant Arup suggests that users leave the system ticking over at night to enable it to quickly get up to normal operating temperature in the morning.
Underfloor heating tends to be more expensive than conventional systems, particularly if fitted retrospectively. In a commercial building, there is less difference in cost between the two types of system than in the domestic sector, as specialists with similar overheads tend to install both types of heating system. Conventional domestic systems are more often installed by an army of small plumbers with low overheads, who can easily undercut the underfloor specialists.