How to install Underfloor Heating – Pocketed Polystyrene System

In this video we go into the detail required when installing a Screeded Underfloor Heating system using Pocketed Polystyrene.

Video Transcript

We’re installing the pocketed polystyrene system for screeded floors. This product includes the floor insulation which has pre-cut channels to hold the pipe. So your pipe spacing is already decided, and the pipe is protected from damage during installation. Sometimes this system is selected as less screed is required than with other underfloor heating systems for screeded floors, which also reduces the screed drying time.
As for any screeded floor, your first step is to place edge expansion foam around the room perimeter. This foam has an adhesive backing to stop it shifting after it has been positioned so that gaps don’t open up, and the screed can’t bridge to the wall.

Peel off the backing pulling it from the underside as you go, but don’t remove the scored backing from the top just yet. That’s there to help you trim the foam later when the screed is laid. It’s a good idea to start placing the expansion foam halfway along a straight section. You’ll find it easy to finish when you reach the end.

When you get there, make a square cut, ensuring that the expansion foam strip overlaps the start, so there’s no bear wall. Then give the overlap a final trim.

Now you’re ready to lay the insulation panels. There are channel panels, and then return panels as well as straight connection panels. So first, plan where they’re going to go. Remember, you’ll need channels for pipe to connect back to manifold. And some areas of the room may not have heating pipe, because underfloor heating shouldn’t be installed under permanent fixtures, such as bathroom fixings for example, or in this case – kitchen cupboards.
That’s why we’ve started with plain insulation panels here. They’ll make sure the floor level is the same for the whole room space.

how to install underfloor heating


For the floors heating areas, first lay the end return sections at each end of the room. Then place the main pocketed panels making sure that the machine pipe channels match up with channels in adjacent sections or with the end return loops. When you need to cut panels to size, measure and mark the trim, then use a hand saw or power tool to make the cut.
Or with thinner panel options, you may be able to use a utility knife. The edge expansion foam has an integral gaiter to stop the screed getting underneath the insulation. So now, go all the way around the room edge to check the gaiters lying flat over the top of the panels. At corners, slit the gaiter, so that it can sit properly.

Now you’re ready to place the pipe into the pre-cut channels in the polystyrene insulation. Remove the Wavin cutter from the pipe coil packaging, and strip off the blue outer wrapping. Find the pipe end from the center of the coil, and feed out the pipe from here.
When you start to install the pipe, make sure you leave a tail long enough to connect back to the proposed location of the manifold. Start at the edge of the room, and clip the pipe over the gaiter to hold it in place. Then continue pushing the pipe into the channels, either by hand or by walking the pipe into place. It’s usually easier to do it by hand at the turns, but quicker to press piping by foot on the straight runs. At corners, roll the pipe into the curve to secure it firmly. When the pipe tails are below the manifold location, clip the pipe into a curved pipe support to hold it securely in position.

When all the pipe has been put into place, you can move on to the final installation stages; including pressure testing of the circuit, installation of the manifold, and pipe connections to it. And once you’ve screeded the floor, you can wire up the controls, and set the thermostats. All of these stages are covered in our other installation videos.

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