How to Wire a Digital Room Thermostat

What You'll Need

It is relatively easy to wire a digital room thermostat provided that you follow all the instructions provided in the kit. The wiring procedure will all depend on the type of room thermostat that you purchase as there are two-wire and three-wire combinations available. Remember to also inspect the backing plate on your digital room thermostat as the plate will indicate the instructions and the corresponding wires that need to be installed.

Remember that mercury-bulb thermostats would need to be properly leveled prior to installation. Negating this procedure will produce an inefficient thermostat reading inside your home. New thermostat systems that rely on other sensing devices other than mercury-bulb will not have a similar problem when it comes to the level procedure.

Step 1 – Shut Down Power Source

Turn off all electrical power that is involved in the HVAC system inside your home. It is important to turn off the power source before wiring a digital room thermostat to prevent the risks of injury, fire, electric shock or equipment damage. This will also allow you to touch the bare edges of the wires without risk of electrocution.

Step 2 – Wire the Digital Room Thermostat

Install the red wire from the heater or air conditioner to the “R” terminal located on the backing plate of the digital thermostat. The white wire from the heater or air conditioning unit should be installed on the “W” terminal as indicated on the backing plate.

For a three-wire digital thermostat combination or series 20 installation, connect the red wire from the heater or air con to the “R” terminal on the backing plate followed by the white wire installed in the “Y” terminal. Next, install the blue wire to the “W” terminal as indicted on the back plate.

Step 3 – Install the Thermostat Body

Tighten the screws that hold the thermostat body and the backing plate in place using a screwdriver. On some thermostat models you might need to plug in a connector between the thermostat body and the mounting plate. Consult the instruction manual as provided by the manufacturer to determine the right procedure that is fit for your digital thermostat.

Step 4 – Turn on the Power

Turn on the power source and the heater or air conditioning system and test the digital thermostat. Adjust the temperature controls as necessary and observe the heating or cooling performance of your system.

If you happen to be using a mercury-bulb type of thermostat and you notice a loss of heating or cooling efficiency, you'll want to inspect the level of the thermostat. Mercury-type digital thermostats have a level line indicated on the backing plate. This means that the thermostat must be aligned according to the level mark on the backing plate. Turn off the power and loosen the screws of the thermostat body and the backing plate before inspecting the level of the thermostat. Adjust the level when necessary.

It is important to keep the manual that comes with the digital thermostat kit. This will help you diagnose any potential problems in the installation procedure.