Things You'll Need
Phillips head screwdriver
Single-pole heater-mounted thermostat
There are numerous ways to wire an electric baseboard heater, depending on your heating configuration and whether you are connecting a single-pole or double-pole thermostat. The most straightforward method for an electric baseboard heater is wiring the heater to an attachable single-pole baseboard thermostat. Notice that you will be working with three sets of wires: the electrical supply wires (black, white and green); the electric baseboard wires (two black and a green); the single-pole thermostat wires (one black and one red). Keep this in mind as you work.
Turn off power to the circuit at the circuit breaker.
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Remove the wiring compartment cover from the electrical supply side of the baseboard heater.
Connect the green ground wire of the baseboard heater and the green ground wire of the electrical supply cable with a wire nut. Twist the wire nut firmly in a counter-clockwise direction until the wire nut is secure. Tape the wire nut to the wires with electrical tape, to ensure that the wire nut does not loosen or fall off in the future.
Look inside the baseboard heater's wiring compartment box for two black wires connected by a small wire nut. Remove the wire nut to disconnect those two black heater wires.
Take the single-pole thermostat and notice the two wires: one is red and one is black. Take the red thermostat wire and connect it to the black wire from the electrical supply cable. Screw on a wire nut in a counter-clockwise direction until the wire nut is secure. Tape the wire nut to the wires with electrical tape.
Take the single-pole thermostat black wire and connect it to one of the baseboard heater's black wires. Screw on a wire nut in a counter-clockwise direction until the wire nut is secure. Tape the wire nut to the wires with electrical tape.
Take the other black wire of the baseboard heater and connect it to the white wire from the electrical supply cable. Screw on a wire nut in a counter-clockwise direction until the wire nut is secure. Tape the wire nut to the wires with electrical tape.
Tuck the wires into the baseboard heater compartment box. Attach the thermostat to the baseboard heater with a Phillips head screwdriver and the screw that has been supplied with the thermostat unit.
Turn the power on at the circuit panel.
A new baseboard heater may emit smoke and a strong burning smell for the first few times of use. This is the protective grease burning off the metal fins of the heater, and is nothing to be alarmed about.
The 240-volt baseboard heater may only be connected to a 240-volt supply with a double pole circuit breaker in the electrical panel. Failure to meet proper electrical standards can result in electrical shock or fire.
Always turn off power at the circuit panel before attempting any electrical work.