underfloor heating

How to Install Underfloor Heating Under Tiles: A Step-by-Step Guide

Gabriel

03 Jan 2026 — 3 min read

Electric underfloor heating under tiles is one of the most satisfying bathroom upgrades — warm tiles underfoot transform the feel of a bathroom more than almost any other single change. Electric mat systems are well within DIY capability for laying and connecting, though the electrical connection to the thermostat requires either a Part P-registered electrician in England and Wales, or DIY notification to Building Control.

Electric vs. Hydronic: Which Is Right?

This guide covers electric heating mat systems — the appropriate choice for retrofitting under bathroom and kitchen tiles. Hydronic (water-based) underfloor heating is primarily installed under a screed during new builds or full renovations; retrofitting it requires significant structural work and is a job for a specialist.

Electric mat systems are thin (2–3mm) heating cables mounted on a fibreglass mesh mat, laid directly in the tile adhesive bed. They heat quickly (15–20 minutes), are thermostatically controlled, and are appropriate as supplementary heating in bathrooms and kitchens. They're not typically intended as the primary heat source for a room.

Choosing the Right Mat

Select a mat based on the area to be heated and the required wattage density:

Bathrooms: 150–200 W/m² (tiles heat quickly; you want warmth within 15–20 minutes)
Kitchens: 150–160 W/m² (lower density acceptable as the floor is heated more continuously)

The mat should cover the area where you actually stand (not under fixed furniture or baths). A 3m² mat is typical for a standard UK bathroom. Brands: Warmup, Nuheat, Wuxly, Devi. Expect to pay £80–200 for the mat, with thermostat an additional £50–150 (or £150–400 for a WiFi-enabled smart thermostat).

Planning the Layout

Roll out the mat dry to plan the installation before mixing any adhesive. The mat can be cut across the fibreglass mesh (not the cable) to change direction and fit around obstacles — never cut the heating cable itself. Plan the route so the cable tail (cold lead) runs to the wall where the thermostat box will be positioned.

The thermostat sensor probe should run between the cable loops in the mat, not under any tiles or furniture — it measures floor temperature directly above the heating element.

Installation Process

Prepare the substrate: The subfloor must be clean, dry, and level. Prime with diluted PVA if porous (concrete or cement board).
First adhesive coat: Apply a 3–4mm layer of flexible tile adhesive (such as BAL Rapid Flex One or Mapei Keraquick) with a notched trowel over the area to be covered by the mat. Embed the heating mat cable-side down into the adhesive.
Run the cold lead: Channel the cold lead (the connection cable from the mat to the thermostat) up the wall in a cable channel (chase) to the thermostat position. Ensure the cold-to-hot joint (where the heating cable meets the connection lead) is bedded in adhesive, not in the wall channel.
Install the sensor probe: Lay the sensor cable in the conduit or channel provided (most kits include an orange conduit) between the first and second heating cable loop. Feed the other end of the sensor to the thermostat position.
Test before tiling: Connect the mat temporarily (using a plug if it's a 13A type, or have your electrician check continuity) and verify resistance readings match the mat's specification. This is non-negotiable — once tiled over, a broken cable is a very expensive repair.
Second adhesive coat and tiling: Apply a second full coat of adhesive over the mat and tile in the normal way. Use a notched trowel to ensure adhesive fully encapsulates the cable. Check that no cable loops are bridging above the adhesive — all should be well embedded.

Electrical Connection

A bathroom underfloor heating system requires:

A fused spur or dedicated circuit from the consumer unit (Part P notifiable work — requires a registered electrician in England and Wales)
The thermostat must be positioned outside Zone 1 (beyond 0.6m from any shower head or bath rim, at a height above 2.25m from the floor) or use a thermostat rated for zone 1 use
The circuit must be protected by a 30mA RCD

First Use and Commissioning

Do not run the heating mat until the adhesive and grout have fully cured — minimum 7 days, preferably 14 days. Running heat through uncured adhesive causes it to dry too rapidly and can crack. Start on a low setting and gradually increase over the first few days of use.