Underfloor heating basics: water systems, electric mats and manifolds

Underfloor heating (UFH) warms a room from the floor up instead of from a radiator on the wall. It has become common in kitchen extensions, bathrooms and new builds. There are two quite different kinds: water (often called "wet") systems that run warm water through pipes, and electric systems that use heating cables or mats. This guide explains the difference and who does what. It is an explainer, not an installation guide.

Water underfloor heating

A water UFH system runs plastic pipe in loops under the floor. Warm water from the home's heating system flows through the loops and warms the floor, which warms the room.

The main parts are:

• Pipe loops, laid in a screed, in grooved insulation boards, or between joists on spreader plates under a timber floor.
• A manifold, usually on a wall or in a cupboard. It splits the flow into the individual loops and brings it back. Each loop normally has its own valve, often with a small flow meter.
• A mixing or temperature control, because UFH runs at a lower water temperature than a typical radiator. Many manifolds include a pump and a blending valve to set this.
• Room thermostats and wiring centre, which open and close the loops for each zone and call for heat.

Water UFH ties into the rest of the heating system. Exactly how it connects depends on the heat source, the other radiators and the controls. That connection is a design decision for a heating engineer. On a gas-fired system, any work on the boiler itself is for a Gas Safe registered engineer. See when to call a Gas Safe engineer and our explainer on combi, system and regular boilers.

Water UFH generally suits new floors, extensions and whole-floor projects, because the pipes and insulation add depth to the floor build-up. It can also work well with heat pumps, which run most efficiently at lower water temperatures.

Electric underfloor heating

Electric UFH uses heating cables, usually fixed to a mesh mat, or thin heating films. They sit just under the floor finish, often tiles. A thermostat with a floor sensor controls them.

Electric systems are thinner and simpler to lay than water pipes, so they are common in bathrooms and small rooms where a water system would mean digging up the floor. The running cost depends on electricity prices and how much the floor is used.

Connecting electric underfloor heating is electrical work for a qualified electrician. It needs a suitable supply, protection and a thermostat connection. In bathrooms and wet rooms the special location rules for electrics apply. In England, electrical work in homes falls under Part P of the Building Regulations. Some work must be notified to building control or done by an electrician registered with a competent person scheme. Read the Approved Document P page on GOV.UK for the official position, and ask your electrician what applies to your job. We do not give wiring instructions.

Laying the mat itself is often described as a DIY-friendly job in product literature. Even so, the floor preparation, insulation board, cable testing before and after tiling, and the final connection all have to be right. Many makers' guarantees depend on the installation being done and tested as they specify.

Design matters more than the parts

Underfloor heating has to be designed for the room. A designer works out:

• the room's heat loss, so the floor can deliver enough heat. A floor can only put out so much before it becomes uncomfortably warm. In a room with high heat loss, UFH alone may not be enough;
• the floor construction and covering. Thick carpet and underlay, or some wood floors, slow heat getting into the room;
• pipe spacing and loop lengths for a water system, or the cable layout for an electric one;
• insulation under the heating, so the heat goes up and not into the ground;
• controls, so each zone can be set separately.

Our radiator sizing guide explains heat loss and why online rules of thumb are only a rough check. The same applies to UFH.

Commissioning and handover

A water UFH system has to be filled, purged of air, pressure-tested and balanced when it is installed, and screeds need to be dried out gently before the heating is run at full temperature. An electric system's cables need to be tested before and after the floor is laid. These are specialist steps. Ask your installer for:

• the design or layout drawing showing where the loops or cables run;
• the commissioning or test records;
• the manifold and thermostat instructions;
• the maker's warranty documents.

Keep these with your house papers. They make fault-finding, and avoiding the pipes when fixing anything to the floor, much easier later.

Living with it

• UFH warms up and cools down more slowly than radiators. Many people run it on a steadier, longer schedule.
• Do not cover large areas of a heated floor with thick rugs or furniture without solid legs.
• Do not drill, screw or nail into a heated floor without knowing where the pipes or cables run.
• If a zone stops heating, check the room thermostat and its batteries first. Beyond that, call the installer or a heating engineer. Do not open the manifold controls or the wiring centre unless the maker's user instructions tell you how.

Our guide to hiring a plumber explains how to find the right trade. A water system needs a heating engineer, and an electric system needs a qualified electrician. For a bathroom project, the bathroom refit order shows where the floor heating fits in.

Which is cheaper to run, water or electric underfloor heating?

It depends on your heat source, energy prices, the floor area and how you use it. Water systems on an efficient boiler or heat pump are usually chosen for larger areas. Electric is often chosen for small rooms. Ask an installer for running cost estimates based on your house.

Can I fit electric underfloor heating myself?

You may be able to lay the mat if you follow the maker's instructions exactly. The electrical connection must be made by a qualified electrician, and Part P applies in England.

Can underfloor heating replace all my radiators?

Sometimes, if the rooms' heat loss is low enough and the floors suit it. A heat-loss calculation and a proper design will show whether each room can be heated by the floor alone.