Underfloor Heating Pipe Calculator — How Much Pipe Do I Need?

Standard domestic installations use 150mm centres, which provides a good balance of heat output and pipe usage. Use 100mm centres for rooms with high heat loss (conservatories, rooms with lots of glazing) or when using a heat pump with lower flow temperatures. Use 200mm centres for well-insulated rooms or supplementary heating.

For 16mm pipe (the most common domestic size), the industry-standard technical maximum is about 100m per circuit; for 20mm pipe it is approximately 120m. Many installers design to a more conservative 80–90m to keep pressure drop low and flow well balanced, so this calculator splits 16mm circuits at 100m by default — you can lower the limit using the Max Loop Length Override in Advanced Options. Exceeding the maximum causes excessive pressure drop and uneven heating, so larger rooms should be split into multiple circuits connected to a manifold.

Yes. Every wet underfloor heating system needs a manifold to distribute water to each circuit (loop) and control the flow temperature. Even a single room needs a manifold if it has multiple circuits. Manifolds are typically sized by the number of circuits — common sizes are 2-port to 12-port.

Yes, but you will need a blending valve (thermostatic mixing valve) to reduce the boiler flow temperature from ~70 °C to the 35–50 °C required for underfloor heating. Alternatively, many modern combi boilers have a low-temperature mode specifically for UFH. Underfloor heating works best with heat pumps which naturally operate at lower temperatures — see our Heat Pump Sizing Calculator and Boiler Size Calculator for help choosing.

PEX or PE-RT underfloor heating pipe typically costs £0.50-£1.50 per metre in the UK, depending on brand and quantity. A 100m coil of 16mm pipe costs roughly £50-£120. Budget quality pipe is at the lower end; premium brands like Rehau, Polypipe, or JG Speedfit are at the higher end. Use our optional price input for a cost estimate.