How to Install Wet Underfloor Heating

An underfloor heating system is an essential for today’s self-builders, yet it can also be installed retrofit. In this article Robbens Systems presents a DIY guide to installing your own ‘wet’ underfloor heating system.

Installing underfloor heating is a popular option amongest self builders. It will allow you total temperature control on a room-by-room basis and because it generates more radiant heat it also reduces drafts, moisture levels and airborne allergens.

When opting for a system, you will need to decide between water (wet) or electric (dry). Water-based systems are suitable for use with solid wood floor finishes, oak for example, because the water flow temperature is low (between 40-60 degrees). Ask your underfloor heating company to tell you floor and room temperatures so that you can check the suitability of your chosen floor finish. Due to the low flow temperatures, wet systems will also complement Renewable heat sources perfectly, such as ground or air source heat pumps.

Whilst wet systems are typically associated with new builds, to allow space for the piping and adequate insulation, they can also be retro-fitted with minimal increase in floor height. They are also inexpensive to install and run.

Here we show you how to install a single room heating pack from Robbens Systems in 10 straightforward steps. These packs come in sizes varying from 14 to 42 square metres. They include a pre-assembled manifold complete with a programmable thermostat, pump, isolation and water temperature control valves and are suitable for screed floors, typically providing an output of up to 100watts per square metre.

1. Clean the sub floor of all debris and add a damp proof membrane (DPM) if necessary. Any sharp irregularities should be removed either by filing, grouting or cutting away.

2. Lay the floor insulation as neatly as possible taking care not to leave large gaps that could fill up with screed. Tape the joints and lay polythene or DPM to stop the screed going under the insulation.

3. Fit the pipe fixing system to the insulation at 90 degrees to the direction that the pipe is going to lay.

4. Mount the manifold on a wall in a suitable location. Check that the surface is strong enough to support the manifold weight and any connecting pipe work. Always mount the manifold before laying pipe work, making sure you work from the manifold with each pipe loop and connect each pipe tail when it is laid.

5. Make sure the underfloor heating pipe is fitted to the flow side of the manifold (this is clearly arrowed) once the end of the pipe has been reamed with the tool provided. This ensures the sealing O-rings are not damaged as the pipe is located onto the joint.

6. The pipe needs to be laid out from the manifold to the furthest point of the room and returned back to the manifold in a ‘snake-like’ pattern with approximately 200mm spacing between each run of pipe. Larger rooms may have two or three loops of pipee in them and each loop should be laid in approximate equal lengths (not exceeding maximum length of circ. 80m). Fix the pipe down by walking it into the clips. The pipe will not be damaged by walking over it, due to its strength and multilayer construction.

7. Once the entire pipe has been installed the system should then be pressure tested with water. This will ensure that there are no leaks in the manifold, joints or pipes. The screed should be laid immediately after and pressure should be left on while this is being laid. A standard sand and cement screed should be laid in accordance with CP8204. It should be well mixed, well compacted, 75mm thick, and cured not dried.

8.The manifold flow and returns must be plumbed in after the boiler pump and before any other radiator or hot water zone valves, allowing the manifold a complete restricted flow and return from the boiler. This must be carried out by a competent plumber.

9. The Robbens Systems underfloor heating pack comes with a programmable room thermostat so that the area can be controlled independently from any other room or hot water system. Again the wiring for the thermostat and boiler connections should be carried out by a competent electrician.

10. The system should not be turned on until the screed has been allowed to cure as turning the heating on too early could damage the screed. The manifolds have an in-built water temperature control and should be run first at a lower setting to allow the screed and floor finishes to warm up slowly before increasing to its final running temperatures. Start up and final temperatures will be specified by the underfloor heating company.