Maximum underfloor heating loop length
A loop that is too long has too much flow resistance: the pump cannot push enough water through it, and the far end stays cooler. That is why every loop has a length limit.
Recommended lengths
| Pipe (outer diameter) | Longest loop | Area per loop at 15 cm spacing |
|---|---|---|
| 16 mm | up to 100 m | about 12–14 m² |
| 17 mm | up to 120 m | about 15–16 m² |
| 20 mm | up to 120 m | about 15–16 m² |
The loop length includes the leads to the manifold. The further away the room, the less pipe is left for the room itself.
Most manufacturers give similar limits, but check your pipe's data sheet for the exact figure. Cautious designers use 80–90 m for 16 mm pipe.
Split large rooms into several loops
If a room needs more pipe than fits in one loop, it is split into two or more. It is best when they are of similar length: they are easier to balance at the manifold, and the floor warms evenly.
Why loops should be of similar length
Water takes the path of least resistance. A short loop gets too much water, a long one too little. The flow regulators on the manifold even this out, but only up to a point. The closer the loop lengths, the easier the system is to balance.
- Put the manifold as close to the middle of the house as you can: shorter leads, more even loops.
- Leads that run through other rooms heat them too. Keep this in mind in hallways and bathrooms.
- One room, its own loop. Several rooms on one loop cannot be controlled separately.