Underfloor Heating Calculator

Underfloor heating (UFH) distributes heat evenly across a room from beneath the floor surface. There are two main types: wet systems, in which warm water is piped through the floor and connected to a boiler or heat pump, and electric systems, which use heating cables or mats laid beneath the floor. Wet systems are more efficient for whole-house heating, while electric systems are better for individual rooms. Within the electric family, mats suit regular rooms such as bathrooms and kitchens and are the most common UK retrofit, while loose-wire cable is used for irregular shapes and costs more up front. Hot air systems exist but are rare in Britain, being more common in Scandinavia and the US.

Installation costs vary significantly. Electric UFH costs £50-£80 per square metre for materials plus installation, making it affordable for bathrooms and kitchens, and a typical bathroom mat retrofit of 5-10 m² comes to about £400-£900 fitted. Wet UFH costs £100-£200 per square metre installed and is best fitted during new builds or major renovations when the floor is being replaced anyway. As a guide, piping a 100 m² bungalow with pipes, manifold and screed runs to £8,000-£14,000, and adding wet UFH to a typical 25 m² extension costs £4,000-£8,000. Retrofitting a wet system into an existing house is often impractical, because it needs 50-65mm of screed plus insulation, so floor levels rise by 80-100mm and door clearances and stairs become a problem.

Running costs depend on insulation, floor covering and heat source. UFH operates at lower water temperatures (35-45 C against 60-80 C for radiators), making it particularly efficient when paired with a heat pump: a wet system on a heat pump costs 50-70% less to run than the same floor fed by a gas boiler, and a wet system on a gas boiler costs about the same as standard radiators while feeling more comfortable. Electric is a different story. At 26.32p/kWh, the October 2026 cap rate, a typical 100W/m² system running 4 hours a day in a 30 m² room uses 12 kWh and costs about £3.16 a day, which is expensive for whole-house heating. Used sparingly it is cheap: a bathroom mat drawing 200W for 1 hour daily costs roughly 5p a day.

The calculator estimates installation and running costs for a single room or a whole-house setup and compares them against a traditional radiator system. You choose the system type, enter the floor area and the hours of use, and it applies the per-square-metre cost and the electricity price to produce a total install figure, an annual running cost and the premium or saving against radiators. If you are also sizing a boiler or heat pump, its output needs to match the UFH heat output of 50-100 W/m², which is well below what a radiator circuit demands.

Floor covering changes the result more than most people expect. Tile and stone have high thermal conductivity and give the most even heat distribution, engineered wood is designed for the stability UFH demands, and luxury vinyl tile (LVT) combines excellent conductivity with comfort underfoot. Carpet is the worst choice, since it acts as an insulating layer and reduces heat output by 30-50%. Solid wood is not ideal because of expansion and contraction, and laminate is usable only with a UFH-rated underlay. Check the floor manufacturer's UFH compatibility before you install anything.

Building Regulations Part L sets insulation levels that must support the efficiency of the system, and a minimum of 50mm of insulation under a wet floor is typical. A manifold with zone controls gives each room its own thermostat, which matters for efficiency as much as for comfort. NHBC and LABC warranties require a pressure test certificate for wet UFH. Manufacturer warranties typically run 10 years on pipes and 5 years on controls, and they usually depend on installation by an accredited specialist, NICEIC for electric systems or APHC for plumbing, so choosing a certified installer protects the cover as well as the workmanship.