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How to DIY Thermostat Installation (Visual Guide)


Replacing your thermostat typically doesn’t require professional experience. It usually takes under an hour, even if you upgrade to a programmable thermostat. Since it can schedule temperatures to be turned back several degrees when there’s less demand, it can save up to 10% annually on heating and cooling, according to the U.S. Department of Energy.1 

If it’s time to replace your thermostat or start saving energy, here is a simple DIY guide on thermostat installation:

Turn Off the Power

Switch off the circuit breaker powering your heating and cooling system at the main electrical panel. Know the voltage rating for the circuit. Installing the right thermostat and wiring will avoid electrical damage, shock, or fire.

Remove the Old Thermostat


Pop off the cover plate or unscrew it with a screwdriver, depending on the model. The thermostat body and electronics are secured to the wall with screws. Unscrew these and carefully pull out the unit, without disconnecting the wires. Use the marking tabs or attach masking tape to each wire. Where the wire is attached, there should be a letter; on the label, mark the letter corresponding to the terminal. Tape the wires to the wall so they don’t fall back inside when you disconnect them.

Install a C-Wire

For smart thermostat installation, you’ll need a C-wire, also known as a common wire, which powers the thermostat independent of other appliances. Your HVAC control board, located in the furnace access panel or somewhere near the air conditioner, may already have a C-wire. If so, simply connect it to the new thermostat.

When you don’t have a C-wire, a power extender kit can enable you to add one. It may be included depending on the model; simply follow the manufacturer’s instructions for installing it. A 24-volt adapter with a C-wire can be used as well. Rather than connecting to a thermostat’s voltage terminals, the adapter plugs into a power outlet. 

Alternatively, an electrician can install the C-wire to a terminal on the HVAC control board.

Install the New Thermostat’s Faceplate

For most thermostats, the faceplate attaches to the wall in the same way. Fasteners should be included in the package. Use the mounting screw holes as references for marking where to drill. Then drill 3/16 inch holes and insert drywall anchors. Separate the new thermostat from the base and screw the base into the wall, using a level to make sure it’s aligned properly.

Connect the Thermostat Wiring

Match each wire to the appropriate screw terminal. The labels you made previously should help with this step. Then connect and secure the low-voltage wires to the base. The owner’s manual should have an installation diagram to guide you. Make sure each terminal screw is tight and install any batteries if your thermostat requires them. 

Mount the Thermostat 

Gently insert any excess wiring into the wall opening. Fiberglass insulation should be used to seal any gaps. It is fire resistant and avoids drafts. Secure the thermostat to the base with screws, if necessary, or snap it in place. Now you can turn the circuit breaker back on, press the reset button, and program the thermostat. Test it to ensure it works with your HVAC system.

Contact Waldrop for Assistance

If you’re having difficulty connecting or mounting your thermostat, Waldrop will be glad to help with thermostat installation. Our technicians can quickly complete installation, make sure the work is done right, and address anything that goes wrong with the thermostat after installing it. To get started or request other professional air conditioning services, contact us online or call 864-536-0887.

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A friend recommended Waldrop after he had a visit last week. Our A/C was not cooling as well as it should, and the Split “Smart” thermostat was doing crazy things on the first and 2nd


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