Plumbing & Heating Calculators

The UK plumbing and heating industry covers everything from domestic boiler replacements to complete central heating system designs. With gas boilers still heating the vast majority of UK homes, correctly sizing your heating system is essential for both comfort and energy efficiency. All gas work must be carried out by a Gas Safe registered engineer, and the installation must comply with the relevant Building Regulations, particularly Approved Document J (combustion appliances) and Approved Document L (energy conservation).

When specifying a new boiler, the kW output must match the property's heating and hot water demand. A typical three-bedroom semi-detached house in the UK requires a combi boiler rated between 28kW and 35kW, though this depends on the number of radiators, bathrooms, and the overall heat loss of the building. Our boiler size calculator helps you determine the right output. Leading UK boiler brands include Worcester Bosch, Vaillant, Baxi, Ideal, and Viessmann, all of which offer models rated for different property sizes.

Radiator sizing is calculated in BTUs (British Thermal Units) based on room dimensions, insulation levels, and window area. Each room in the house needs a radiator (or radiators) that can deliver enough heat to overcome heat losses through walls, windows, floors, and ceilings. Our radiator sizing calculator accounts for these factors using standard UK heat loss calculation methods.

The growing adoption of heat pumps (air-source and ground-source) is reshaping the UK heating landscape. Under the Boiler Upgrade Scheme, homeowners in England and Wales can receive grants of up to £7,500 towards the cost of a heat pump installation. Heat pumps operate at lower flow temperatures than gas boilers (typically 35–45°C versus 60–80°C), which means radiators often need to be larger or underfloor heating used instead. Our heat pump sizing calculator helps estimate the capacity required for your property based on its heat loss characteristics.

For pipe sizing, UK domestic plumbing typically uses 15mm copper or plastic (JG Speedfit, Hep2O) for individual supplies, 22mm for main distribution, and 28mm for high-flow applications. Correct pipe sizing ensures adequate flow rates to all outlets while maintaining acceptable pressure drop. All plumbing work must comply with the Water Supply (Water Fittings) Regulations 1999, which govern the design, installation, and maintenance of water systems in UK buildings.