What cable size do I need for underfloor heating?

Supply cable size depends on total zone load. A 15m² zone at 150W/m² = 2.25kW = 10A - 2.5mm² cable on 16A circuit is fine. Larger zones or multiple zones from one circuit may need 4mm² on 20A or 6mm² on 32A. Calculate your total wattage first.

How do I calculate UFH electrical load?

Multiply heated area (m²) by watts per m² (typically 150-200W). Example: 20m² × 150W = 3000W = 3kW. Convert to amps: 3000W ÷ 230V = 13A. Add 20% safety margin for larger supplies.

Can I run multiple UFH zones from one circuit?

Yes, if total load allows. Add up all zone wattages and ensure circuit can handle total current. A 16A circuit handles about 3.5kW total, 20A handles 4.5kW, 32A handles 7kW. Separate thermostats still needed per zone.

What MCB rating for underfloor heating?

MCB rating depends on total load. Single small zone: 16A. Multiple zones or large areas: 20A or 32A. Type B MCBs are suitable for resistive heating loads. Each circuit needs 30mA RCD protection.

Do I need RCD protection for underfloor heating?

Yes, 30mA RCD protection is required for all UFH circuits under BS 7671. This is especially critical for bathroom installations. The RCD can be at the consumer unit (RCBO) or a separate RCD protecting the circuit.

What about bathroom underfloor heating zones?

Bathroom UFH must comply with BS 7671 Section 701 (special locations). 30mA RCD protection mandatory, and installation must consider zones around baths and showers. IP-rated thermostats required if within zone 2.

Can electric UFH work with a heat pump?

Electric UFH is different from wet UFH systems used with heat pumps. Electric UFH has heating cables in the floor; wet systems have water pipes. Some properties use electric UFH in bathrooms alongside a heat pump for main heating. They require separate electrical supplies.

How many zones can I have on one circuit?

As many as the circuit can handle electrically. A 16A circuit at 230V = 3680W maximum. Three 10m² zones at 150W/m² = 4500W - too much for 16A. Either use 20A/32A circuit or split into separate circuits.

Do I need a dedicated circuit for UFH?

Dedicated circuits are recommended, especially for larger installations. Small single zones might work from existing circuits if capacity allows, but this is not best practice. Dedicated circuits ensure reliable operation and easier fault finding.

What thermostat do I need for electric UFH?

Electric UFH requires thermostats rated for the zone load - typically 16A models. Programmable thermostats save energy. Floor sensor probe thermostats prevent overheating. Smart thermostats offer remote control. Each zone needs its own thermostat.

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Underfloor Heating Cable Sizing Calculator

Calculate the correct supply cable size for electric underfloor heating systems

Electric UFH Cable Quick Facts

Electric UFH typically 150-200W per m² heating output
10m² room at 150W/m² = 1.5kW = 6.5A per zone
Multiple zones often need separate circuits or higher rated supply
Thermostat/timer required for each zone
RCD protection mandatory - 30mA for bathroom zones

Cable Size Calculator

BS 7671:2018+A2:2022 compliant

1. Load Current

2. Cable Length (meters)

3. Installation Method

Lighting circuit (3% voltage drop limit)

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Common UFH Installations

Single zone bathroom (5m² at 150W/m²)

16A circuit, 2.5mm² cable sufficient

Single zone kitchen (15m² at 150W/m²)

16A circuit, 2.5mm² or 4mm² cable

Multiple zones from one circuit

Calculate total load - may need 20A or 32A circuit

Large open-plan area (30m²+)

Split into zones, consider separate circuits

Extension/conservatory UFH

Check total property load - may need consumer unit upgrade

Related Heating & Bathroom Installations

Electric UFH is often installed alongside other bathroom electrical work. You might also need our electric shower cable calculator for the same project. For whole-house heating with wet UFH, see our air source heat pump calculator - heat pumps work brilliantly with wet underfloor heating systems.

Electric Underfloor Heating Cable Sizing

UFH supply cable sizing determines the conductor cross-sectional area (mm²) needed to safely supply electric underfloor heating systems. Unlike the thin heating cables embedded in the floor, the supply cable from consumer unit to thermostat must be sized for the total zone load. Multiple zones increase total current demand.

UFH Electrical Installation Costs (2024)

Typical UK electrical supply installation costs. Does not include UFH mats/cables or floor preparation.

Installation Scenario	Materials	Labour	Total
Single zone UFH supply (<10m²)	£50-100	£100-180	£150-280
Multiple zone UFH supply (10-30m²)	£100-200	£150-280	£250-480
Large installation (30m²+)	£180-350	£250-400	£430-750
Thermostat per zone	£50-150	£40-80	£90-230 per zone
Consumer unit upgrade	£150-300	£200-350	£350-650

Prices as of 2024. Smart thermostat options cost more but offer energy savings.

UFH Heating Cables vs Supply Cables

Electric UFH uses two types of cable: (1) Heating cables/mats embedded in the floor - thin, specific resistance, supplied by manufacturer. (2) Supply cables from consumer unit to thermostat - standard cables sized for total zone load. This calculator helps with supply cable sizing, not the heating cable itself.

UFH Wattage Calculation

Electric UFH output is measured in watts per square metre (W/m²). Typical values: 150W/m² for well-insulated rooms, 200W/m² for bathrooms or poorly insulated spaces. Total load = heated area × W/m². Note: heated area excludes areas under fixed furniture and fittings.

Zone Control Strategy

UFH zones allow different areas to be heated independently with separate thermostats. Typical zoning: bathrooms on early morning timers, living areas on evening schedules, bedrooms separately controlled. Each zone needs thermostat and potentially separate circuit for larger installations.

Frequently Asked Questions

Related Electrical Calculators

Electric Shower

Often paired with bathroom UFH

Air Source Heat Pump

Ideal for wet UFH systems

Voltage Drop Calculator

Check long cable runs

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