Install the New Thermostat Base
Remove the base from the new thermostat and position it on the wall where the previous thermostat was located. Use a level to make sure it is straight so the internal sensor will be accurate.
Mark the wall through the mounting holes on the base.
Remove the base and use your marks for reference to drill holes for mounting. Use a drill bit slightly smaller in diameter than the screws you'll be using.
Stuff the hole around the furnace control wires with a piece of paper towel. This prevents drafts, which could affect the thermostat's performance.
Feed the wires through the base of the thermostat, and screw the unit into position. If you're mounting the thermostat to drywall, use the drywall anchors supplied with the new thermostat kit.