Replacing a Thermostat: Four Types and the Steps to Install One

Which thermostat fits the way you live?

A new thermostat can save energy and money, and The Home Depot's walkthrough starts by sorting the choices into four main types. A non-programmable thermostat is simple to adjust and suits people who are rarely away from home. A programmable thermostat lets you pre-set the temperature with daily and weekly settings, which is ideal for climates with big temperature changes. A Wi-Fi thermostat lets you check and adjust the temperature from a smartphone, useful for controlling the home while away. A smart thermostat goes one step further and learns your heating and cooling behavior; it can also be managed from other smart devices.

The installer demonstrates with a smart thermostat, noting that most steps are the same whichever type is being installed.

Power off and check the voltage

The first step is to turn off power to the HVAC at the electrical panel. Before buying or fitting a replacement, make sure it does not exceed the voltage of the current circuit, since that could be a potential fire hazard. Removing the face of the old thermostat lets you confirm the voltage is compatible. Also check that the existing wires are compatible with the new thermostat.

Photograph, disconnect and remove the old base

Before touching the wires, take a photo of them. It records which terminal each wire went into. The wires can then be unscrewed from their terminals, taking care that they don't fall back into the wall. After that the old base plate comes off.

Mount the new base

If the new thermostat doesn't cover the old holes, patch them first. In this install a trim plate is used to hide the old holes on the wall. The new base is screwed to the wall, and a level is used to make sure it is straight before the mounting is finished.

Connect the wires

The wires go to their matching terminals on the new mounting plate. On this thermostat, you push a button down to attach each wire; other models may require the wires to be screwed in place. The video also shows how this looks on other types. For programmable and non-programmable units, you push the button down and insert the wires into the right terminals. On a Wi-Fi unit, the wires are fed into the terminals until they click into place.

Finish and restore power

The thermostat control unit mounts to the base by snapping into place. Power to the HVAC is then restored at the electrical panel, and the thermostat is operated according to the manufacturer's instructions.