Electric Underfloor Heating: Regulations, Installation & Opportunities

Electric underfloor heating is a growing market for electricians, driven by the shift towards heat pumps and away from gas boilers. Underfloor heating works efficiently at lower flow temperatures than traditional radiators, making it the ideal distribution system for heat pumps. As the UK moves towards its 2035 gas boiler phase-out target, demand for underfloor heating installations is increasing steadily.

There are two main types of underfloor heating: electric (dry) systems that use heating cables or mats, and water-based (wet) systems that circulate warm water through pipes in the floor. This guide focuses on the electrical aspects — circuit design, regulations, testing, and the business opportunity for qualified electricians.

Electric underfloor heating is particularly popular for retrofit projects, notifiable installations in bathrooms, kitchens, and extensions where running pipework for a wet system would be impractical or too expensive. It adds minimal height to the floor build-up and can be installed quickly.

There are three main types of electric underfloor heating element, each suited to different floor types and room shapes.

Heating Mats

Pre-spaced heating cable fixed to a fibreglass mesh mat. These are the most popular option for regular-shaped rooms with tiled floors. The mat is rolled out directly onto the subfloor or insulation board, and tiles are laid on top using flexible tile adhesive. Heating mats are thin (typically 3 to 4mm) and add minimal height to the floor build-up.

• ✓Best for: bathrooms, kitchens, and regular-shaped rooms with tile or stone floors
• ✓Typical output: 150W to 200W per square metre
• ✓Easiest to install — cable spacing is pre-set by the manufacturer
• ✓Minimal floor height increase (3 to 4mm plus tile adhesive)

Loose Cable

Individual heating cable that is laid out manually and fixed in place with clips or laid into a self-levelling compound. Loose cable offers flexibility for irregular room shapes, around obstacles, and in areas where mats cannot be cut to fit. Cable spacing determines the heat output per square metre.

• ✓Best for: irregularly shaped rooms, around obstacles, and custom layouts
• ✓Typical output: 150W to 200W per square metre (depending on cable spacing)
• ✓More labour-intensive to install than mats
• ✓Greater flexibility in coverage and heat output

Foil Systems

Ultra-thin foil heating elements designed for installation under laminate, engineered wood, and vinyl flooring. Foil systems are dry-installed — no adhesive or screed is required. They sit on top of insulation boards and directly beneath the floor covering.

• ✓Best for: laminate, engineered wood, and luxury vinyl tile (LVT) floors
• ✓Thinnest option — typically under 2mm
• ✓Dry installation with no adhesive or levelling compound required
• ✓Lower output per square metre (typically 140W to 160W) due to floor temperature limits

Electric underfloor heating should be supplied from a dedicated circuit from the consumer unit. A thermostat controls the system, switching the heating element on and off to maintain the set temperature. Most thermostats also have a floor sensor to limit maximum floor surface temperature.

Load Calculations

The electrical load depends on the heated area and the output rating of the heating element. For example, a 10 square metre bathroom at 150W per square metre has a total load of 1500W, drawing approximately 6.5A at 230V. A 20 square metre kitchen at 200W per square metre draws 4000W (approximately 17.4A).

• ✓Small bathroom (5m2 at 150W/m2): 750W — approximately 3.3A at 230V
• ✓Standard bathroom (10m2 at 150W/m2): 1500W — approximately 6.5A at 230V
• ✓Kitchen (20m2 at 200W/m2): 4000W — approximately 17.4A at 230V
• ✓Living room (30m2 at 150W/m2): 4500W — approximately 19.6A at 230V

Cable Sizing and Circuit Rating

Cable sizing is based on the design current of the circuit, taking into account the installation method, ambient temperature, grouping, and insulation. A typical bathroom underfloor heating circuit can be supplied by a 2.5mm2 cable on a 16A or 20A MCB. Larger areas with higher loads may require 4mm2 or 6mm2 cable.

Where the total load exceeds 3.6kW (approximately 16A), consider splitting the heated area into multiple zones on separate circuits. This also improves temperature control and reduces the impact of a circuit fault.

Related Course

18th Edition (2382)

Circuit design for underfloor heating requires knowledge of BS 7671 regulations and cable sizing.

View Course

Under the 18th Edition Amendment 2, 30mA RCD protection is required for all circuits in a domestic installation. Underfloor heating circuits are no exception. This protection can be provided by an RCBO at the consumer unit (recommended for best practice) or by an RCD protecting the relevant bank of circuits.

RCD protection is particularly important for underfloor heating because the heating element is embedded in the floor structure. If the cable insulation is damaged — for example by a screw or nail penetrating the floor — an earth fault could develop. The 30mA RCD will detect this fault current and disconnect the supply before it becomes dangerous.

• ✓30mA RCD protection is mandatory for all domestic circuits under BS 7671 Amendment 2
• ✓RCBO protection recommended so a fault only affects the underfloor heating circuit
• ✓RCD protects against cable damage that may not be immediately apparent
• ✓The RCD test button should be demonstrated to the customer after installation

Correct installation is critical for both performance and safety. The heating element must be installed in accordance with the manufacturer's instructions, and the electrical connection must comply with BS 7671.

Floor Preparation and Insulation

Good insulation below the heating element is essential for efficiency. Without insulation, a significant proportion of the heat is lost downwards into the subfloor rather than warming the room. Insulation boards (typically 6mm to 10mm thick) are installed on top of the subfloor before the heating element is laid.

Heating Element Placement

• ✓Heating elements must not be installed under fixed furniture (kitchen units, built-in wardrobes)
• ✓Maintain clearance from walls — typically 50mm to 100mm
• ✓Do not overlap heating cables or mats — this causes hot spots and cable failure
• ✓Leave sufficient cold tail length to reach the thermostat position
• ✓Route the floor sensor between two heating cables, not directly over a cable

Thermostat and Floor Sensor

The thermostat is typically mounted on the wall at standard accessory height. It controls the heating element via a relay or triac and monitors both air temperature and floor temperature (via a floor sensor embedded in the screed or adhesive between two heating cables). The floor sensor limits the maximum floor surface temperature, which is essential when wood, vinyl, or laminate floor coverings are used.

• ✓Mount the thermostat at standard accessory height (1.2m to 1.4m)
• ✓Install the floor sensor in conduit so it can be replaced if it fails
• ✓Position the floor sensor centrally between two heating cables
• ✓Set the floor temperature limit according to the floor covering manufacturer's specification
• ✓Programmable or smart thermostats can significantly reduce running costs

Testing underfloor heating installations combines manufacturer-specific cable tests with standard BS 7671 electrical tests. Thorough testing at each stage of installation is essential because faults become extremely difficult and costly to fix once the floor covering is in place.

Heating Cable Tests

The heating cable resistance should be measured at three stages: before installation (to confirm the cable is undamaged from the factory), after laying the heating element (to confirm no damage during installation), and after the floor covering is fitted (to confirm no damage during tiling or other floor work). The manufacturer supplies the expected resistance value, and the measured value should be within the manufacturer's stated tolerance (typically plus or minus 5 to 10 per cent).

• ✓Measure cable resistance before installation — record the value
• ✓Measure cable resistance after laying — compare with pre-installation reading
• ✓Measure cable resistance after floor covering is installed — compare again
• ✓Compare all readings with the manufacturer's stated resistance value
• ✓A significant change in resistance indicates cable damage

Standard Electrical Tests

In addition to the cable-specific tests, the standard BS 7671 electrical tests must be carried out on the completed circuit.

• ✓Continuity of protective conductors
• ✓Insulation resistance (minimum 1 megaohm at 500V DC)
• ✓Polarity
• ✓Earth fault loop impedance (Zs)
• ✓RCD operation — 30mA trip within required time
• ✓Functional testing — thermostat and floor sensor operation

Related Course

18th Edition (2382)

Understanding testing requirements and BS 7671 compliance is essential for underfloor heating installations.

View Course

Electric underfloor heating represents a growing revenue stream for electricians. The market is driven by several converging factors that are increasing demand year on year.

Market Drivers

• ✓Heat pump adoption — underfloor heating is the most efficient distribution method for heat pumps, which operate best at lower flow temperatures
• ✓Gas boiler phase-out — the UK government's target to end new gas boiler installations by 2035 is accelerating the shift to heat pumps and electric heating
• ✓Retrofit demand — electric underfloor heating is popular for bathroom and kitchen renovations, where wet systems are impractical
• ✓New build specification — increasing numbers of new homes are specified with underfloor heating as standard
• ✓Energy efficiency regulations — tighter building regulations are driving demand for efficient heating systems

Adding It to Your Services

For a qualified electrician, adding underfloor heating installation to your service offering is straightforward. The circuit design and electrical connection use standard skills. The main additional knowledge is around heating element selection, floor preparation, and working with floor fitters and tilers. Many electricians partner with tiling contractors to offer a complete package.

A typical domestic underfloor heating installation (bathroom or kitchen) can be quoted at 400 to 800 pounds for the electrical work, depending on complexity and location. This includes the circuit from the consumer unit, thermostat installation, connection of the heating element, and testing and certification. The heating element and thermostat are typically supplied by the customer or included as a separate line item.