How to wire a thermostat for a 220v heater

Written by allen teal
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How to wire a thermostat for a 220v heater
Using wire nuts makes a safe electrical connection. (wire nuts image by Paul Moore from

The thermostat for 220-volt electric heaters is a line-voltage thermostat. This means that the 220 volts that power the heater also pass through the thermostat. Unlike low-voltage thermostats that operate on 24 volts, working inside these thermostats can involve serious danger if the power is not shut off. Whether you are dealing with a new installation or replacing an existing thermostat, this job is not difficult but must be done correctly for function and safety.

Skill level:

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Things you need

  • 220 volt thermostat
  • Screwdriver
  • Screws, 2
  • Wire nuts, 2
  • Wire strippers

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  1. 1

    Turn off the breaker for the circuit with the thermostat and 220-volt electric heater. If you are uncertain about which circuit to shut off, turn off the main breaker to the house. Inside the switch box, you should see two wires that run from the electric heater: one is black; the other is either white or red. Strip about one inch of the insulation from the ends of each wire with wire strippers.

  2. 2

    Pull the knob from the thermostat off its stem to remove it. Grip the cover of the thermostat and pull it off. Inside you should see a red and black wire. Fasten the black wire from the heater to the red wire on the thermostat. The white or red wire from the heater will attach to the black wire from the thermostat. Twist the ends of the wires together and screw a wire nut onto each connection.

  3. 3

    Push the wires gently into the switch box. Insert the body of the thermostat into the box until the tabs at the top and bottom are touching the outside of the box. Using a screwdriver, install the screws that came with the thermostat to attach the thermostat to the switch box. Snap the cover back onto the thermostat and slide the knob back onto the stem.

  4. 4

    Restore power to the circuit. Turn the thermostat up until you hear a click that signals it has turned on the heater. Wait about five minutes and check the heater to make sure it is warming. Set the temperature to the desired level.

Tips and warnings

  • Always turn off the power before installing a thermostat.

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