How much pipe underfloor heating needs
The amount of pipe depends on three things: the heated area, the pipe spacing and how far the room is from the manifold. Enter your numbers, or use the formula below.
The formula
Pipe in the room ≈ area (m²) ÷ spacing (m). At 15 cm spacing every square metre takes 1 ÷ 0.15 ≈ 6.7 m of pipe.
| Spacing | Pipe per m² | For a 20 m² room |
|---|---|---|
| 10 cm | 10 m | 200 m |
| 15 cm | 6.7 m | 133 m |
| 20 cm | 5 m | 100 m |
Don't forget the leads
Every loop starts and ends at the manifold. If a room is 6 m from the manifold, each of its loops needs another 12 m of pipe: 6 m to the room and 6 m back. With many loops, the leads are a large share of the total.
A worked example
A 20 m² living room, 15 cm spacing, manifold 5 m away. The room itself takes about 133 m of pipe; with 10 m of leads the loop would be 143 m. That is over the 100 m limit for 16 mm pipe, so the room is split into two loops of about 77 m each (67 m in the room plus 10 m of leads). In total, about 153 m.
How much to buy
- Add 5–10% spare for bends, detours and offcuts.
- Each loop is laid from one unbroken length, with no joints in the floor, so choose coils that give whole loops.
- The calculator gives an estimate. The exact length depends on the room shape, doors and where the manifold is.