Underfloor heating calculator — pipe length and loops

Pipe length = (area ÷ spacing) × (1 + allowance/100). Example: 20 m², 15 cm spacing, 10% allowance: (20 ÷ 0.15) × 1.10 ≈ 147 m.

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.

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.

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.

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.

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.

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.

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.

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.

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%.