Underfloor heating pipe calculator
With underfloor heating the pipe length follows directly from the area and the spacing between pipe runs: closer spacing means more pipe and more even heat.
Your measurements
Result
- Pipe length (no reserve)
- 133 m
- Pipe to order (+10%)
- 147 m
Closer spacing gives more even heat but needs more pipe. Split long runs into circuits of at most about 80–100 m.
How the calculation works
- Pipe length (m) = area (m²) × 100 ÷ pipe spacing (cm).
- Length to order = pipe length + 10% reserve for bends and manifold connections.
Worked example
For 20 m² at 15 cm spacing: 20 × 100 ÷ 15 = 133 m of pipe; with a 10% reserve you order about 147 m.
What the calculator assumes
- 15 cm spacing is usual in living rooms; 10 cm in bathrooms and along external walls, 20 cm in less demanding spaces.
- The area is the free area: no pipe goes under fitted units or the bath.
When to adjust the result
- A 16 mm pipe circuit shouldn't exceed about 80–100 m, so the calculated length is split into several circuits, each with its own manifold connection.
- Runs from the room to the manifold are added if the manifold is far away.
- The floor finish matters: tiles transfer heat best; thick wood flooring and rugs slow it down.
Planning underfloor heating
Underfloor heating works at low flow temperatures, which suits heat pumps and condensing boilers, but it depends on insulation underneath so heat goes up rather than into the ground. Keep each circuit within the maximum pipe length the manufacturer gives (often around 80–100 m for 16 mm pipe) and use closer pipe spacing near cold external walls.
Floor coverings matter: tiles and stone conduct heat well; thick carpet and wood with high thermal resistance slow the system down. Screed needs to cure and then be heated up gradually following the manufacturer's heating-up protocol before the floor covering goes on.
Frequently asked questions
How much pipe per m² of underfloor heating?
About 6.7 m per m² at 15 cm spacing and 10 m per m² at 10 cm spacing, plus a reserve.
How long can an underfloor heating circuit be?
With 16 mm pipe, usually up to about 80–100 m; longer runs are split into separate circuits.
Wet or electric underfloor heating?
Wet systems are cheaper to run for whole floors with a heat pump or boiler; electric mats are cheap to install for small rooms such as a bathroom but cost more to run.
Can underfloor heating go under wood?
Yes, with engineered or approved boards and a limited surface temperature; check the product's suitability and total thermal resistance.