Installing Underfloor Electric Mats

This story shows how to install underfloor electric mats for radiant heat.

Step 1

Make sure you can drill through the floor and the bottom plate of the wall directly below the thermostat. Drill a hole through the subfloor and wall plate for the switch/thermostat wiring. Clean out any waste in the hole with a 1/2-inch chisel.

Step 2

Cut the mat to fit the spaces between the joists (some mats have dotted cut lines). At one end of each mat, strip 3/4 inch of insulation from the power wires. With a helper, staple the mat to the subfloor with 1/2-inch staples.

Step 3

Connect the wires together according to the manufacturer's instructions. Splicing sleeves are a quick and easy method to make secure connections. Strip about 1/2 inch of insulation from the ends and slide the bare wire into a splicing sleeve. Squeeze the sleeve with wire crimpers.

Step 4

Cut a 3-inch piece of electrician's tape and, starting at the insulation, wrap the tape tightly around the sleeve. Make sure to cover the joint from the insulation at one end of the sleeve to the other. Fasten the bare wires at the end mat to the circuit wires and tape these joints.

Step 5

Before installing the junction box, push fish tape through the hole in the floor plate. If your helper can't grab the end of the tape after a couple of attempts, try hooking the tape with a bent coat hanger. Pull the tape through the hole with the wiring. Install insulation between the joists.

Step 6

Remove the knockouts on the junction box and slide the box over the wires toward the wall. Fasten the box to the wall using its tabs or screws and tighten any wiring clamps inside the box. Attach the wires to the switch or thermostat with wire nuts.


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