In-screed electric underfloor heating

In-screed electric heating

In-screed electric heating sits at the bottom of a 20 to 25 mm screed bed, which is then tiled or finished over. It can be laid on a structural slab, on fibre cement sheet, or on F-Board insulation where the floor needs to come up to temperature quickly.

Two options cover most jobs. The MK 200 mat has the cable pre-laid at 80 mm spacing on a 500 mm wide light fibreglass mesh, which makes the set-out quick and even. Loose CK 17 cable is the better answer for rooms with an awkward shape, because the spacing can be set to the area available.

Both are twin conducting and generate very low electromagnetic frequency, and both come with a 3 m cold tail that can be made to length where the thermostat is a long way from the floor.

Installation

The floor is set out first so the cable stays clear of the shower waste, the toilet pan and anything else that will be drilled or cut later. Cable is fixed down with clips or steel fixing strips at 600 mm centres, or the mat is rolled out and the mesh cut to turn it.

A floor sensor is run into a conduit between two cable runs so the sensor can be replaced later without lifting tiles. The screed then goes down over the top.

A licensed electrician connects the thermostat on its own circuit with residual current protection. We test the cable for resistance and insulation before and after the screed so any damage is found immediately.

Under timber, the lower output CK 10 cable at 10 watts per metre is used instead, to keep the surface temperature within what the boards will take.

Things to consider

• Needs a 20 to 25 mm screed bed over the cable
• MK 200 mat is rated at 200 watts per square metre
• CK 17 cable is rated at 17 watts per metre
• CK 10 at 10 watts per metre for under timber
• F-Board insulation cuts warm-up time and running cost
• Suits a flat rate or a time-of-use tariff

Installation photos

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