Underfloor heating calculator

Order too little pipe and you're back at the merchant mid-install. Order a wildly generous margin "just in case" and you've tied up cash in coiled pipe that sits in the van for months. This calculator gives a working figure — pipe length and loop count — from floor area and spacing, so you can order close to what you'll actually use.

Spacing sets the pipe run

Tighter spacing means more pipe per square metre and a more even floor temperature — useful in rooms with high heat loss or poor insulation below. Wider spacing uses less pipe and is common around room perimeters or in less demanding spaces. 150mm is the everyday default for most UK living spaces; 100mm shows up in bathrooms and conservatories; 300mm is typically reserved for perimeter runs rather than the main field.

Why the manifold distance is doubled

The figure you enter is the one-way distance from the manifold to the room. Every loop needs a flow pipe going out and a return pipe coming back, so that distance gets counted twice before it's added to the pipe laid across the floor itself. Skip this and the length you order comes up short the moment you start connecting up.

Why loop count matters

Push too much pipe through a single loop and the pressure drop gets high enough that flow suffers at the far end of the run — the room heats unevenly, or the pump can't keep up. This calculator assumes a conservative 100m maximum per loop, splitting the total pipe length across enough loops to stay under that. Actual maximum loop length varies by pipe bore and manufacturer, so check the spec for the pipe and manifold you're actually fitting.

What this doesn't cover

Real rooms aren't perfect rectangles. Bay windows, chimney breasts, awkward corners and the serpentine pattern pipe actually follows all add waste the straight-line formula doesn't capture. Build in a sensible margin for offcuts and bends, and check manifold port count against the number of loops before you commit to an order.