What Size Cable Do You Need for Electric Underfloor Heating?
For electric underfloor heating up to 3.6kW (16A at 230V), use 2.5mm² cable on a dedicated 16A circuit under BS 7671. Under NEC, 12 AWG on a 20A circuit is standard per Table 310.16. Larger areas requiring over 16A should be split into multiple zones, each with its own circuit and thermostat.
Quick Reference: Cable Size for Electric Underfloor Heating (UFH) by Standard
| Standard | Cable Size | Conditions | Reference |
|---|---|---|---|
| BS 7671 | 2.5mm² | 16A dedicated circuit, Method C | Table 4D1A |
| NEC | 12 AWG | 20A circuit, THWN-2 | Table 310.16 |
| AS/NZS 3008 | 2.5mm² | 16A dedicated circuit, AS/NZS 3000 | Table 13 |
| IEC 60364 | 2.5mm² | 16A dedicated circuit | Table B.52.4 |
Values shown are for copper conductors in typical domestic/commercial conditions. Actual size depends on installation method, ambient temperature, and cable length. Use our free cable sizing calculator for your exact scenario.
Typical Applications for a Electric Underfloor Heating (UFH)
- Bathroom underfloor heating
- Kitchen UFH mat
- Conservatory floor heating
- En-suite underfloor heating
Calculate Your Exact Cable Size
These are general guidelines. Your specific installation needs exact calculation accounting for cable route length, installation method, ambient temperature, and cable grouping.
Frequently Asked Questions
Does underfloor heating need a dedicated circuit?▼
Yes. Electric UFH should have a dedicated radial circuit from the consumer unit. BS 7671 requires this for fixed heating appliances. Each zone with its own thermostat typically needs its own circuit for proper control.
What size circuit for a bathroom UFH mat?▼
A typical bathroom UFH mat (2-4m²) draws 300-600W (1.3-2.6A). A 16A circuit with 2.5mm² cable is more than adequate. The thermostat contactor is the switching device — ensure it matches the mat's current rating.
Can I run multiple UFH zones on one circuit?▼
Only if the total load is under 16A (3.6kW). Multiple small bathroom mats totalling under 3kW can share a circuit. Larger installations should have separate circuits per zone for independent thermostat control and fault isolation.
Does UFH need RCD protection?▼
Yes. Under BS 7671, electric underfloor heating installed in bathrooms requires 30mA RCD protection (Regulation 701.411.3.3). For other rooms, RCD protection is recommended and often required by the manufacturer.
What is the difference between supply cable and heating cable?▼
The supply cable (2.5mm²) connects the consumer unit to the thermostat. The heating cable (embedded in the floor) is the UFH element itself — typically rated at 150-200W/m². These are completely different cables with different specifications.
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