Underfloor Heating Installation

The parts of a wet underfloor heating system, in plain English

• Pipework: flexible plastic pipe laid in loops under the floor. Warm water runs through it and the floor becomes the radiator.
• Manifold: the metal unit, usually in a cupboard, where every loop starts and ends. Each loop has its own valve so each room can be controlled separately.
• Mixing valve: on the manifold. It blends hot water from the boiler with cooler return water so the floor runs at around 35 to 45 degrees rather than the 60 to 70 a radiator gets.
• Circulation pump: on the manifold, pushes the water round the loops.
• Zone actuators: small motors on the manifold that open and close each loop when its room thermostat calls for heat.
• Room thermostats: one per zone. Set the temperature you want in each room.
• Wiring centre: the box that connects the thermostats to the actuators and tells the boiler when to fire.
• Insulation: the board under the pipes. Without it, half the heat goes into the ground.
• Screed or overlay: the floor over the pipes. Screed is poured on a new floor; overlay boards sit on an existing one.
• Heat source: your boiler or a heat pump. The manifold connects to it like one big radiator.

What's involved in the installation

• Survey and design: the floor is measured, the heat loss of each room worked out, and the pipe spacing set: closer together for a cold room or a bathroom, wider for a well insulated lounge.
• Insulation and pipework: insulation boards go down, then the pipe is clipped in loops at the designed spacing. A whole ground floor is a day or two of pipe laying.
• Manifold and connections: the manifold is fitted, every loop connected, and the whole system pressure tested before anything covers the pipes. This is the point of no return, so it's done properly.
• Floor goes down: screed poured by the builder, or overlay boards laid by us. Screed then needs to cure, usually a few weeks, before the heating is run.
• Commissioning: the system is filled, each loop balanced so every room heats evenly, the thermostats set up and the heating brought up to temperature in stages so the floor isn't shocked.

Honest advice: what's overkill

• Underfloor heating upstairs “to match”: bedrooms are used at night with the heating off. Radiators upstairs and underfloor downstairs is cheaper and works better.
• A new boiler as part of the job: most combi and system boilers run underfloor heating fine through the mixing valve. Only replace the boiler if the survey shows it's too small or too old, not because a salesman said so.
• Smart thermostats in every room: one smart controller for the system is useful. Smart stats in every zone is money that would be better spent on thicker insulation under the pipes.
• Electric mats in a big room: cheaper to fit, expensive to run. Anything bigger than a small bathroom should be wet.
• Worth paying for: the insulation board. It's the cheapest part of the system and the one that decides whether your running costs are low or high for the next thirty years.

When to ask for a survey

The best time is before the floor goes down, while the builder is still on site. If you're planning an extension, a kitchen or bathroom refit, or a floor that's coming up anyway, message us with the room size and the stage you're at. Book a free survey