How to Replace a Manual Thermostat

Manual thermostats control the furnace by turning it on and off to meet the setting the thermostat is set to. They typically have an analog dial and aren't automated in any way. Most of these thermostats are being replaced by digital programmable ones due to the desire for more energy saving measures. While some people may call a heating and air conditioning technician to replace a manual thermostat, it is a task the typical homeowner can do himself.

  1. Turn off the power to the furnace by turning off the correct circuit breaker in the circuit breaker panel.

  2. Pull the manual thermostat off the wall plate with gentle pressure. Disconnect the thermostat wires from the thermostat, and label each one with the letter of the terminal it is connected to.

  3. Unscrew the wall plate from the wall with a screwdriver to remove it. Install the new wall plate, and secure it with drywall anchors and screws.

  4. Look over each individual thermostat wire. Check that it is stripped to show 1/4 inch of bare copper. If there is excess, clip it off; if there isn't enough, strip each wire further.

  5. Connect each thermostat wire to the new thermostat. Refer to the labels to ensure you are connecting them to the correct terminals.

  6. Push the thermostat onto the wall plate until it clicks into place. The wall plate has plastic tabs that will lock into the thermostat.

  7. Turn the power back on to the furnace. Read the thermostat's instruction manual thoroughly, and set the temperature to the desired setting.


  • The control board of the furnace can be damaged if the power is not disconnected prior to replacing the thermostat. Always make sure the power is off before working on any component of the furnace.
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