Underfloor Heating Calculator: Pipe Length and Manifold Circuits
Enter the room's net area and the pipe spacing to instantly see the length of underfloor heating pipe needed and how many circuits (outlets) the manifold requires.
Factor: 10 m/m² · For preliminary estimates only.
How Is It Calculated?
The pipe is laid on the floor at equal spacing. The smaller the spacing, the more pipe per square meter and the more even the heat distribution. Pipe length per square meter is the inverse of the spacing: at 10 cm spacing, 1 ÷ 0.10 = 10 m.
| Pipe spacing | Pipe per m² | 20 m² room | Circuits |
|---|---|---|---|
| 10 cm | 10 m | 200 m | 3 |
| 12.5 cm | 8 m | 160 m | 3 |
| 15 cm | 6.7 m | 134 m | 2 |
| 20 cm | 5 m | 100 m | 2 |
The number of circuits is calculated assuming a maximum circuit length of 75 m. This tool is for preliminary estimates; a final design requires a room-by-room heat loss calculation and a circuit plan.
What Determines the Cost?
- Total pipe length and pipe type
- Number of manifold outlets and equipment (flow meters, valve group)
- Insulation panels and edge strip (equal to the net area)
- Screed, fittings and labor
For details on per-square-meter costs and system selection, see our underfloor heating cost guide.
Products for Your Calculation
Choose the manifold, pipe and fittings based on the number of circuits you calculated:
How do you adjust the flow on a manifold? Guide to adjusting a manifold with flow meters · What does a manifold with flow meters do?
Frequently Asked Questions
How do I calculate underfloor heating pipe length?
Multiply the net area by the pipe length per square meter for the chosen pipe spacing. Length per square meter is 1 ÷ pipe spacing: 10 m at 10 cm spacing, about 6.7 m at 15 cm spacing. For example, a 20 m² room needs about 200 m of pipe at 10 cm spacing.
How long should an underfloor heating circuit be?
The longer the circuit, the higher its pressure loss. Our calculator assumes a maximum circuit length of 75 m and finds the number of circuits by dividing the total pipe length by 75 and rounding up.
How many outlets does the manifold need?
Each circuit connects to one flow and one return outlet on the manifold, so the manifold needs as many outlets as there are circuits. The number of circuits in the calculator shows how many outlets you need.
Need a material list for your project?
Send us your area and floor plan, and we will work out the pipe, manifold and fittings together.