How to Hard Wire a Home Thermostat

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Things You'll Need

  • Multimeter

  • Thermostat

  • Screwdriver

  • Small level

Modern hardwired thermostats offer control options never seen on older models.

Hardwired thermostats offer features such as programmable settings, touch screen controls and filter monitors. Hardwired units draw their power from an external power supply, thus relieving homeowners from the hassle of battery replacement that stems from wireless thermostats. Hardwiring a thermostat to the heating and cooling appliances throughout the home is not a difficult task for individuals with an understanding of basic electrical wiring.


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Step 1

Read the instructions that came with the thermostat. The configuration may deviate from a more common one and learning a little is always a good thing. Read the manual that came with the furnace to ensure that your system is compatible and to see clearly where to place wires.

Step 2

Turn off the power to the furnace. Shut off switches look like a light switch but are located near the furnace and on the ceiling or clearly marked on the wall. Test the power with a multimeter at the furnace to ensure power is off. If there is any problem locating the switch, turn the power off at the circuit breaker.


Step 3

Lift the faceplate of the thermostat off and look to see how many wires are coming out. There are devices that convert two wires to four or five, but if the thermostat requires more wires than available, a professional should be brought in and/or new wiring run from the furnace to the thermostat.

Step 4

Secure the wire colors according to the thermostat instruction. The standard setup begins with the red wire going to the RH, which usually has a jumper from there to the RC. Green connects to G and powers the fan for times when only the fan is running. Yellow wires connect to Y and controls the air conditioner. Finally, the white wire connects to W and controls the heat.


Some systems have additional wires. This is where reading the instructions comes in handy. Some furnaces may require a common wire that is black or blue and connects to the common in the furnace. This is usually required on thermostats that are digital or mechanical with an indicator light.

Step 5

Secure the thermostat to the wall. Make sure that it is level and positioned properly.

Step 6

Open the furnace door and locate the circuit board. Connect the wires to the furnace. A wiring diagram is located on the inside of the door and shows the layout if you run into difficulty. The same letter to color options should be present on the circuit board as found in the thermostat.

Step 7

Secure the furnace door and turn on the power