Project Guide

How to Install a Thermostat

Turn Off Power to the HVAC System
Turn power off to HVAC
  • Before you begin to change the thermostat in your home, turn off the power for your heating and air-conditioning system at the main service panel. 
  • Remove the old thermostat cover plate with a screwdriver.


Tip: Screwdriver sets come with a variety of head types to fit various fixtures in your home.

Remove the Old Thermostat
Illustration of someone removing an old thermostat
  • Unscrew the thermostat mounting screws and remove the thermostat body. 
  • Label the low-voltage wires to identify their screw-terminal locations using masking tape and then disconnect the wires. There is no standard color code, so use letter codes to make the wires easy to identify.
  • Remove the thermostat base by loosening the mounting screws. 
  • Tape the wires to the wall or wrap them around a pencil to prevent them from slipping into the wall cavity.
Install the New Thermostat
Illustration of someone installing a new thermostat

Safety note: Do not use on your thermostat on circuits exceeding manufacturer-specified voltage. Higher voltage thermostat wiring will damage the controls and may cause shock or become a fire hazard. Additionally, short or incorrect thermostat wiring will the damage unit and may cause personal injury and/or property damage. 

  • Separate the front of the new thermostat from the base. Begin by installing the base first.
  • Thread the low-voltage wires through the specified opening of the new thermostat base. 
  • Use a small level to make sure it’s properly aligned.
  • Mount the thermostat base on the wall using the screws included with the thermostat. 
  • Connect the low-voltage wires to the appropriate screw terminals on the new thermostat base 
  • If your connections do not match, consult the installation diagram in the new thermostat's owner's manual. 
  • Optional: Locate the low-voltage transformer that powers the thermostat. The transformer is usually located near the heating and air-conditioning system or inside of a furnace access panel.
  • Tighten any loose wire connections and make sure the wires and sheathing are in good condition. 
  • Install the battery or batteries in the thermostat body (if applicable). Make sure the battery size and polarity are both correct.
  • Mount the thermostat base by gently pushing the excess wire back into the wall opening and plugging the hole with a fire-resistant material. Fiberglass insulation is great for preventing drafts from affecting thermostat operation. 
  • Mount the control unit to the base using the screws included with your thermostat. Tighten the screws securely. 
  • Restore power to your heating/cooling system, then press the reset button to clear the program memory.
  • Program the thermostat according to the manufacturer's instructions.
  • Test the unit to make sure both the furnace and air conditioning unit are cycling properly.
Thermostat Wiring Tips
A hand touching the base of a thermostat
  • Installation varies for two-wire systems (heating only or cooling only). 
  • If you have a two-wire system, refer to the instructions manual provided by the manufacturer for a more detailed installation guide. 
  • Tighten any unused terminals securely.
  • If your system has more than two wires, follow the manufacturer installation diagram to determine correct wire connections. 
  • Heating and cooling needs vary from season to season, so adjust the programming as needed to accommodate your lifestyle.
  • If you have more than one heating or cooling system, placing an adjustable thermostat on each one will ensure greater energy efficiency.