Electric Underfloor Heating: Circuits, RCDs and Certificates

Electric underfloor heating is popular in London bathrooms, kitchens and extensions, where it frees up wall space and keeps tiled floors warm. It is a simple system, but it still needs the right circuit, protection and paperwork. This guide explains what an electrician looks at before, during and after installation.

Mats, cables and the right circuit

Most electric underfloor heating uses thin heating mats or loose cables laid under the floor finish, controlled by a thermostat with a floor sensor. A small bathroom mat may be fed from an existing circuit through a fused connection unit, if that circuit has enough spare capacity. Larger areas, such as a whole kitchen or extension, usually need their own dedicated circuit from the consumer unit. The installer should check the load before deciding.

RCD protection

Underfloor heating must be protected by a 30 mA RCD, and in bathrooms this is essential. Older consumer units often lack suitable RCD protection, so a board upgrade may be needed first. Our guide to fuseboard replacement in London explains when.

Testing during installation

Good practice is to test the heating cable or mat before it is laid, after it is laid, and again after the tiles or floor finish go down, recording the results. A damaged cable under new tiles is expensive to put right, so these checks matter. Keep the test results and the manufacturer's warranty card together.

Notification and certificates

A new circuit, or new work in a bathroom, is notifiable under building regulations. You should receive an Electrical Installation Certificate for a new circuit or a Minor Works certificate for an addition to an existing one. Our guide to EICR, EIC and Minor Works certificates explains which you need.

What an EICR often finds

• Underfloor heating with no RCD protection.
• Large mats added to a socket circuit that was already well loaded.
• No certificates or test records for the heating at all.
• Thermostats fitted inside bathroom zones where they should not be.

Our guide to bathroom electrics and zones explains where controls can go.

Book a check

Energy North Ltd covers North, East and West London with City & Guilds certified electricians, and can usually attend within 48 hours. See our EICR service.