Calculator
Underfloor loop calculator
How many metres of pipe and how many loops - measured from real geometry, not a formula.
Enter the room dimensions, the pipe spacing and the distance to the manifold. You get the loop drawn, the pipe length inside the room, the length of the run to the manifold and the number of circuits needed. For a rectangular room this is not an estimate - it is the same algorithm that draws loops in the HeatAlgo app.
Underfloor heating loop length
Enter the room dimensions, the pipe spacing and the distance to the manifold. The answer comes from the same algorithm that draws loops inside the HeatAlgo app.
Example - enter your own room above to calculate yours
The loop in this room
- Pipe in total
- 92.6 m
- Loops needed
- 1
- Pipe in the room
- 77.0 m
- Run to manifold
- 15.6 m
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This calculation covers a rectangular room. L and T shapes, slanted walls, obstacles and several rooms on one manifold are handled in the app.
How it works
You give four numbers: room width and length, pipe spacing, and the one-way distance to the manifold.
The algorithm traces the loop around the real room outline, with a setback from the walls and real pipe bend radii - and measures length from the drawn geometry rather than from floor area.
The run to the manifold is added: out to the room and back again. That is the most common reason a loop that fits the limit on paper does not fit once installed.
The result shows pipe inside the room, the run to the manifold, the total and the loop count. L and T shapes, slanted walls, obstacles and several rooms on one manifold are handled in the app.
Questions and answers
Common questions about loop length
How many metres of pipe per square metre of underfloor heating?
About 10 m/m² at 10 cm spacing, about 6.7 m/m² at 15 cm and about 5 m/m² at 20 cm. That is the pipe inside the loop field only - the run to the manifold has to be added, out to the room and back again. At a manifold 15 m away that adds roughly 30 m to every loop.
Is the (area ÷ spacing) × 1.1 formula correct?
It is incomplete, and wrong in two opposite directions at once. It overstates the pipe inside the room, because it counts the whole floor area while a loop is never run right up to the wall - HeatAlgo sets it back by 10 cm. At the same time it understates the total, because it contains no term for the run to the manifold. For a 3.2 by 4.0 m room at 15 cm spacing the formula gives 93.9 m wherever the manifold stands, because it never asks. The real pipe inside the room is 77.0 m, and the run is added on top: 15.6 m at a manifold 8 m away, 29.6 m at 15 m - so 92.6 m or 106.6 m in total. The further the manifold, the more the formula understates.
Why does this differ from other calculators online?
Because this one measures geometry rather than floor area. The loop is traced around the real room outline, set back 10 cm from the walls, with real pipe bend radii, and the length is measured from the drawn path. The run to the manifold is then added, which per-square-metre formulas leave out entirely.
What pipe spacing should I use?
Spacing follows from how much heat the floor has to deliver: the tighter the pipe, the more watts per square metre at the same flow temperature. Along external walls and under windows the spacing is tighter than in the middle of the room. The starting point is the room's heat demand from the heat load calculation, not the floor area on its own.
Will it handle an L-shaped room?
No. This calculator covers a rectangular room. L and T shapes, slanted walls, obstacles and several rooms on one manifold are handled in the underfloor heating module inside the HeatAlgo app, on an uploaded floor plan.