How to Make a PEX Barrier How to Make a PEX Barrier

What You'll Need
Extruded Polystyrene
Rebar mesh or foam board staples

A PEX barrier is a layer of a radiant heating system made from PEX tubing that has an oxygen barrier in it. PEX is the shorthand name for cross-linked polyethylene tubing; it’s a type of plastic tubing that hot water can run through to heat a floor. Barrier PEX is the type of PEX with the oxygen barrier in it and it allows a person to use cast iron pieces in a radiant heating boiler and manifold. By keeping oxygen from getting in the system, barrier PEX prevents cast iron parts from rusting. Cast iron is a cheaper and longer lasting material. To create a PEX barrier for an in-floor heating system with cast iron parts, follow these steps.

Step 1 – Level the Area with Gravel

If installing a new floor over bare ground, use gravel to fill and level the area.

Step 2 – Cover the Gravel with Foam

Using 4 by 8 foot pieces of extruded polystyrene, cover the entire floor. The pieces do not need to be seamed together, but tape maybe used to keep them firmly in place while the PEX is attached. This foam board will both prevent cold air from the ground from cooling the slab from below, and keep the warming effects of the radiant heat from being pushed down into the ground.

Step 3 – Attach the Barrier PEX

The PEX should be laid across the floor in a curving zig-zag pattern to ensure the entire slab is heated. There are two ways to attach barrier PEX to the foam board. One way is to roll out a rebar mesh across the foam board. The PEX can be attached to this mesh which will also reinforce the concrete slab when it is poured.

The second way to connect the PEX is to use foam board staples. These staples are long plastic pieces that are barbed in such a way that once they are pushed in, they cannot be pulled back out. There is a special staple gun that will push the staples into the foam board, but many contractors just push the staples in by hand since the staple guns are relatively expensive and not totally necessary.

Step 4 – Connect the PEX and Test the System

Connect the PEX to the supply line and the manifold. Test the system to ensure that water flows through it properly with no stoppages. This is an important step, because once the concrete is poured, it will be virtually impossible to change parts of the system that are sunk within it.

Step 5 – Pour the Concrete

Pour the concrete for the slab over the entire radiant heating system. The barrier PEX should be no deeper in the concrete than 2 inches below the finished floor surface. At this depth the heat from the water flowing through the PEX should easily transfer to the surface of the floor.

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