100mm
- Approx. pipe per m²
- 10m
- Area reached by 100m before manifold feeds
- About 10m²
- Typical design context
- Higher-output zones where the design specifically calls for close spacing
Water underfloor heating advice
How Much Underfloor Heating Pipe Do I Need?
Estimate from the net heated area, designed pipe spacing and the complete route to and from the manifold.
As a quick guide, allow about 5m of pipe per m² at 200mm spacing, 6.7m per m² at 150mm spacing or 10m per m² at 100mm spacing—before adding the manifold connection route.
Quick Pipe Estimate by Spacing
Use these figures for early estimating. Final spacing and circuit length must be confirmed by the property heat-loss and hydraulic design.
| Pipe spacing | Approx. pipe per m² | Area reached by 100m before manifold feeds | Typical design context |
|---|---|---|---|
| 100mm | 10m | About 10m² | Higher-output zones where the design specifically calls for close spacing |
| 150mm | 6.7m | About 15m² | Common residential spacing, subject to the heat-loss design |
| 200mm | 5m | About 20m² | Lower heat-load areas where wider spacing can still meet the design output |
150mm
- Approx. pipe per m²
- 6.7m
- Area reached by 100m before manifold feeds
- About 15m²
- Typical design context
- Common residential spacing, subject to the heat-loss design
200mm
- Approx. pipe per m²
- 5m
- Area reached by 100m before manifold feeds
- About 20m²
- Typical design context
- Lower heat-load areas where wider spacing can still meet the design output
The area figures use the simple relationship between spacing and pipe length. They do not include the pipe needed to travel from the manifold to the heated area and back.
PRACTICAL TOOL
Estimate Your Pipe Quantity
Enter the net heated area, designed spacing and one-way manifold distance. The calculator adds both the flow and return route plus a modest routing allowance.
Indicative estimate
90.7metres of pipe
Pipe in heated area80.4m
Flow and return6.0m
Indicative circuits1
Round the circuit count up, then plan similar loop lengths rather than one very long and one very short circuit.
How to Calculate the Pipe Quantity
Work from a dimensioned floor plan and the designed pipe spacing.
Measure the net heated area
Measure only the floor that will contain pipe. Follow the approved layout around permanent floor-level units, sanitaryware, fireplaces and other fixed obstructions.
Apply the designed spacing
Multiply the net heated area by 10m per m² at 100mm, 6.7m per m² at 150mm or 5m per m² at 200mm.
Add the manifold route
Measure from the manifold to the start of the heated area. Include both the outward and return legs for every circuit.
Allow for the real route
Add a modest allowance for bends and practical routing, then check the result against the maximum circuit length in the system design.
CIRCUIT PLANNING
Worked Example and Circuit Planning
The quantity estimate must still be shaped into practical, balanced circuits.
Worked example
12m² at 150mm spacing
A 12m² heated area uses approximately 80.4m of pipe. With the manifold 3m away, the outward and return route adds 6m. Before a small allowance, the estimate is approximately 86.4m; a design allowance brings it to roughly 90m.
One typical 16mm circuit may be suitable, subject to the specified pipe, heat output, flow rate and pressure drop.
Circuit planning
How Many Circuits Will I Need?
A typical residential 16mm circuit is commonly kept at around 100m or less unless the approved design says otherwise. The total includes the room pipe and both manifold connections.
If the estimate exceeds the permitted length, divide the area into two or more similar circuits. Always round the count up and adjust the layout.
What Can Change the Estimate?
A quick calculation is useful for budgeting, but the pipe is only one part of a working system.
Room heat loss and required output
Pipe diameter, floor construction and pressure drop
Fixed furniture and floor-level units
Extra connection distance from a shared manifold
Designer-specified tighter spacing near glazing
Heat source and planned flow temperature
Water underfloor heating advice
Frequently Asked Questions
Quick answers about coil coverage, circuit length, fixed units and pipe spacing.
Does a 100m coil cover 20m²?
Only at approximately 200mm spacing and before allowing for the route to and from the manifold. At 150mm spacing, 100m covers about 15m² before those connection lengths are added.
Can I make one circuit longer than 100m?
Do not exceed the circuit length stated in the approved system design. Very long circuits increase pressure drop and can be difficult to balance. Splitting the area into similar circuits is normally better.
Should pipe be installed beneath kitchen units?
Follow the designed layout. Pipe is normally kept out of areas beneath permanent floor-level units and other fixed obstructions, while still providing enough heated area to meet the room heat loss.
Is closer pipe spacing always better?
No. Closer spacing uses more pipe and changes the circuit design. The correct spacing delivers the required output with the chosen floor construction, water temperature and heat source.