Underfloor Heating Calculator
Calculate the power of your heating cable or mat, circuit length, laying pitch, supply cable section and circuit breaker rating — taking into account room type, floor covering and IEC 60364 requirements.
What the calculator computes
- Required specific power of the underfloor heating depending on the room type and floor covering
- Total installed power of the circuit in watts and kilowatts
- Length of the heating cable or area of heating mats
- Cable laying pitch in centimetres
- Design current of the circuit and circuit breaker rating
- RCD requirement (30 mA) and thermostat selection
How to choose the underfloor heating power
Specific power (W/m²) is the key design parameter. For comfortable floor heating in living spaces, 100–140 W/m² is enough; for full heating without radiators — 150–180 W/m². In bathrooms and utility rooms the norms are higher: 140–150 W/m² in comfort mode, because tiles require more intensive heating.
Remember: heating cable or mat is laid only on free area — under furniture without legs and stationary plumbing, installation is prohibited; this is both overheating and a direct manufacturer ban (warranty is voided).
For cable systems (heating cable in screed), choose a specific power of 110–140 W/m² with a laying pitch of 8–12 cm. For heating mats, the power is fixed by the manufacturer (usually 150–220 W/m²) and is selected by area. Infrared film floors give 150–220 W/m² and are laid only under laminate, linoleum or carpet without screed.
Calculation formulas
The calculation is based on simple ratios:
1. Required thermal power of the circuit: Q = S_usable × q_specific, where S_usable is the free floor area (m²), q_specific is the specific power (W/m²).
2. Heating cable length: L = S_usable × 1000 / P_linear, where P_linear is the linear power of the cable (usually 16–20 W/m).
3. Cable laying pitch: h = (P_linear / q_specific) × 100, cm. For q = 130 W/m² and a 17 W/m cable, the pitch is about 13 cm.
4. Design line current: I = P / U (for a single-phase 230 V network), I = P / (√3 × U) for three-phase.
5. Breaker rating: I_br ≥ 1.25 × I_design — standard range 6, 10, 13, 16, 20, 25 A. For power up to 3.5 kW on one circuit, a C16 breaker and 2.5 mm² cable are usually sufficient.
Specific power table by room type
| Room | Comfort mode, W/m² | Full heating, W/m² | Covering |
|---|---|---|---|
| Bathroom / WC | 140–150 | 180 | Tile, porcelain |
| Kitchen | 120–140 | 170 | Tile / laminate |
| Hallway / corridor | 120–130 | 160 | Tile / laminate |
| Bedroom | 100–120 | 160 | Laminate / parquet |
| Living room | 100–120 | 160 | Laminate / parquet |
| Balcony / loggia | 140–160 | 200 | Tile |
Regulatory framework
Underfloor heating design is regulated by IEC 60364 (low-voltage electrical installations), HD 60364 series, and in the UK by BS 7671 (IEE Wiring Regulations, Section 753 for floor heating). In the EU, EN 1264 covers water-based systems; electrical systems follow IEC 60364-7-753. Key requirements:
— the heating circuit is fed by a separate line from the distribution board, protected by an RCD with a tripping current of no more than 30 mA;
— allowable floor surface temperature: 29 °C in areas of constant occupancy (25 °C in many countries), 35 °C at room edges and in bathrooms (per BS 7671 and EN 1264);
— the heating cable in the screed is laid only with minimum 30 mm of screed cover or in cable channels — no direct contact with insulation;
— a thermostat with floor sensor is mandatory: without it the floor overheats, consumption grows, and the cable fails.
How to use the calculator
- Select the room type (bathroom, kitchen, bedroom, etc.) — the calculator will suggest the recommended specific power.
- Enter the room area in m² and the share of usable area (70% by default).
- Select the system type: heating cable, heating mat or IR film.
- Press «Calculate» and get the power, length, pitch, current, breaker, RCD and thermostat requirements.
Common installation mistakes
- Laying under furniture and plumbing — overheating and cable failure, void warranty.
- Missing thermostat — 30–50% excess electricity consumption and covering overheating.
- Forgotten RCD — in case of cable damage, electric shock is possible.
- Pitch below 8 cm — local cable overheating in the screed.
- Thin screed (less than 30 mm above the cable) — cracks and uneven heating.
- Power calculated for the whole area without furniture — less real heat than expected.
Underfloor heating FAQ
How much electricity does underfloor heating consume?
In comfort mode — 10–20 W/m² on average per day (including thermostat on/off cycles). Full heating of a 20 m² room consumes 1.5–2.5 kWh per day depending on heat loss. Smart thermostats with floor and air sensors reduce consumption by 30–40%.
Can underfloor heating be used as the main heating?
Yes, if the specific power is 150–180 W/m² and the room heat loss does not exceed the selected power. For well-insulated houses up to 60–80 m², cable floor heating can fully replace radiators. Heat loss calculation is mandatory — use the heat loss calculator.
Why can't the cable be laid under furniture?
Furniture without legs blocks heat dissipation, the cable overheats above the allowable 90 °C for the sheath, the screed cracks, and the manufacturer's warranty is voided. Film floors under furniture are also prohibited.
Which circuit breaker is needed for underfloor heating?
For a circuit up to 3.5 kW — C16 breaker with 30 mA RCD, cable 3×2.5 mm². For 3.5–5.5 kW — separate 16 A circuits or a C25 breaker with 4 mm² cable. The calculator gives the exact values.
What is the difference between a heating cable and a mat?
The cable is laid in the screed with arbitrary pitch and suits complex configurations, but requires 30–50 mm of screed. The mat is a cable on a mesh laid in tile adhesive without screed — minimal floor build-up. Film is laid under laminate/linoleum without screed, but requires insulation beneath it.
Is a permit required for installing underfloor heating?
In apartments, coordination with the management company may be required for work that increases the load. In private houses a permit is not required, but design per IEC 60364 / BS 7671 is mandatory.