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Floor Heating Calculator
System parameters
Room 1
Underfloor heating calculator — loop design and pipe spacing
Professional calculator for designing hydronic underfloor heating systems. Calculates specific floor heat output, surface temperature, loop length, and assesses whether underfloor heating will cover the room's heat losses. Calculations compliant with PN-EN 1264 — accounting for floor covering thermal resistance, pipe spacing, and heating medium parameters.
A tool for designers, installers, and building owners planning underfloor heating in a new building or retrofitting an existing system. For each room, the calculator will assess whether underfloor heating alone is sufficient or if supplementary radiators are needed. Results can be saved to a project and exported as PDF.
How to use the calculator in 3 steps
Set system parameters: supply and return temperatures. For underfloor heating, typically 35–45 °C supply and 28–35 °C return. Remember that supply temperature directly affects floor surface temperature — PN-EN 1264 limits it to 29 °C in occupied zones.
Add rooms: for each one enter heat losses Q [W], heated floor area [m²], room temperature, room type (living room/bathroom/perimeter zone), floor covering, and pipe spacing (100–300 mm).
Read results: the calculator will show specific heat output [W/m²], floor surface temperature, loop length [m], and heat loss coverage assessment. If underfloor heating doesn't cover 100% of losses — reduce pipe spacing or plan supplementary radiators.
What the underfloor heating calculator computes
The program determines all parameters needed for proper underfloor heating loop design:
- q — specific floor heat output [W/m²], resulting from the heating medium temperature, pipe spacing, and floor covering thermal resistance.
- T_floor — floor surface temperature [°C] — the calculator checks whether it exceeds permissible values per PN-EN 1264 (29 °C occupied zone, 33 °C bathrooms, 35 °C perimeter zone).
- L — underfloor heating loop length [m], including the actual heated area and the run from the manifold to the room (2× distance).
- Heat loss coverage [%] — ratio of floor heating output to room heat losses. A value ≥ 100% means underfloor heating alone is sufficient.
- Loop flow rate [l/h] — required heating medium flow, needed for manifold selection and rotameter setting.
Input data — what to enter and where to find it
Supply temperature [°C]
Heating medium temperature at the heat source outlet or after the mixing valve. Typically 35–45 °C. With a heat pump often 35 °C, with a condensing boiler 40–45 °C. Higher supply temperature gives greater heat output but raises floor temperature — don't exceed PN-EN 1264 limits.
Return temperature [°C]
Heating medium temperature returning to the heat source. The supply/return difference (Δt) for underfloor heating is typically 5–10 K. Smaller Δt means more even floor temperature distribution but higher required flow rate.
Heat losses Q [W]
Room heating demand from calculations per PN-EN 12831. Underfloor heating at standard parameters (40/30 °C, 200 mm spacing) delivers about 50–80 W/m². If room heat losses exceed this value, supplementary radiators are necessary.
Heated floor area [m²]
Actual area where heating pipes will be installed — reduced by fixed furniture (kitchen units, built-in wardrobes, bathtub). Typically 60–85% of the room's usable floor area.
Pipe spacing [mm]
Distance between centers of adjacent pipes. Typical spacings: 100 mm (bathrooms, perimeter zone — highest output), 150 mm (rooms with high heat losses), 200 mm (standard for residential rooms), 250–300 mm (well-insulated buildings). Smaller spacing = higher output but longer loops and more pipe.
Floor covering
Type of floor finish affects floor covering thermal resistance. Ceramic tiles — best conductivity (R ≈ 0.01 m²K/W). Parquet/laminate — moderate resistance (R ≈ 0.05 m²K/W). Carpet — highest resistance (R ≈ 0.10 m²K/W). The standard recommends total floor covering resistance ≤ 0.15 m²K/W.
Key considerations for underfloor heating design
Maximum floor temperature per PN-EN 1264: 29 °C in permanent occupied zones, 33 °C in bathrooms, 35 °C in perimeter zones. Maximum single loop length is 120 m (for 16×2 mm pipes, manufacturers recommend up to 100 m) — longer loops cause excessive hydraulic resistance. Screed thickness above pipes: 45–65 mm. If underfloor heating doesn't cover room heat losses, reduce pipe spacing, increase supply temperature, or supplement with radiators.
Related heating system calculators
Underfloor heating is part of a complete heating system. When designing the entire system, you may also find useful:
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How to calculate underfloor heating step by step — guide with calculator