Underfloor heating calculator — pipe length and loops
The underfloor heating calculator computes the total length of heating pipe needed for a floor zone and estimates the number of hydraulic loops. Enter the heated area, pipe spacing (in metres) and a percentage allowance for bends and installation losses to get indicative material quantities for planning your underfloor heating system.
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How we calculate pipe length
Formula: pipe length = (area ÷ spacing) × (1 + allowance / 100). Spacing determines layout density — smaller spacing means more pipe and higher heating power. The allowance (typically 10%) covers bends, manifold connections and installation waste. Number of loops = total length ÷ 120 m, rounded up.
Example calculation
Room 20 m², pipe spacing 15 cm (0.15 m), allowance 10%. Base length: 20 ÷ 0.15 = 133.3 m. With 10% allowance: 133.3 × 1.10 ≈ 146.7 m of pipe. Number of loops (max 120 m/loop): ⌈146.7 ÷ 120⌉ = 2 loops.
Frequently asked questions
How do I calculate pipe length for underfloor heating?
Pipe length = (area ÷ spacing) × (1 + allowance/100). Example: 20 m², 15 cm spacing, 10% allowance: (20 ÷ 0.15) × 1.10 ≈ 147 m.
What pipe spacing should I choose?
10 cm for high heat-loss zones (bathrooms, perimeter strips); 15 cm for typical living rooms; 20 cm for well-insulated buildings with low heat demand. Smaller spacing means more pipe and more heat output.
How many loops does underfloor heating need?
Each loop should not exceed 80–120 m (depending on pipe diameter) to limit hydraulic resistance. The calculator uses a 120 m maximum and rounds up. Each loop connects to a manifold port.
What pipe types are used for underfloor heating?
Most common: PE-RT (polyethylene raised-temperature resistance) and PEX (cross-linked polyethylene), typically 16×2 mm or 20×2 mm. Pipes with an EVOH oxygen-barrier layer prevent oxygen ingress and corrosion of metal components.
What supply temperature is used for underfloor heating?
Underfloor heating operates at low supply temperatures: 35–45°C (versus 60–80°C for radiators). Floor surface temperature should not exceed 29°C in occupied zones and 33°C in perimeter zones.
How much does underfloor heating cost in Poland?
Approximate costs: materials (pipes, manifold, expansion tape, foil) 25–50 PLN/m²; labour 30–60 PLN/m²; screed 30–60 PLN/m². Total: 85–170 PLN/m². For an 80 m² flat: 7,000–14,000 PLN.
How long does the screed take to dry?
Anhydrite screed: approximately 1 day per 1 mm thickness at 20°C and 65% humidity — about 50–60 days for a 55 mm screed. Before commissioning, run a drying programme: raise supply temperature by 5°C/day up to 50°C, then hold for 3–4 days.
Can underfloor heating be used under any floor covering?
Yes, but with limitations. Ceramic tiles and natural stone are ideal. Laminate and engineered wood must be marked "suitable for underfloor heating". Solid parquet needs expansion gaps. Carpets limit efficiency. Floor thermal resistance must not exceed 0.15 m²K/W.
What is the difference between serpentine and spiral (snail) layouts?
Serpentine (meander): pipe runs in parallel loops — simpler to install but the supply end is warmer than the return. Spiral (bifilar): supply and return pipes alternate — more even temperature distribution, recommended for living areas. Spiral uses about 10% more pipe.
How do I balance underfloor heating after commissioning?
Balancing is done at the manifold using thermostatic valves or electric actuators controlled by room thermostats. Each zone should have its own thermostat. Hydraulic balancing — setting flow in each loop — is best done by an installer with a flow meter. A programmable weekly thermostat can reduce energy use by 15–25%.
Results are indicative and apply to a single heated zone. A full underfloor heating system design should be carried out by a qualified installer taking into account the building's heat demand, floor construction and manifold hydraulic parameters.