How to Install a Digital Programmable Thermostat

A person adjusting a programmable thermostat on the wall.
What You'll Need
Masking tape
Torpedo level
Cordless drilldriver
Instruction booklet

When you install a digital, programmable thermostat it gives you access to a variety of settings for regulating the temperature in your home. You can schedule the heat or AC to kick on exactly when you want it to and keep it off during the hours you are at work or not at home. Installing one is not only easy to do, but it can ultimately save you money on your heating and cooling bills.

Note: If you live in an area where you also need a humidistat in your home, you will need to to know basic installation instructions for that as well.

Step 1 – Turn Off the Power

Before you remove your old thermostat, find the breaker that powers the circuit and switch it off.

Step 2 – Remove the Old Thermostat

Take off the cover. Depending on the model, this may simply pull off or there may be screws holding it in place that you must remove first. With the cover off, remove the screws that hold the thermostat to the mounting plate, and carefully pull it out.

Disconnect the wires attached to the thermostat and wrap them around a pencil to keep them from falling through the hole in the wall. As you remove each, use the masking tape to label it with the letter assigned to its current terminal. Then, remove the mounting plate as well.

Step 3 – Install the New Mounting Plate

Position the new thermostat's mounting plate over the hole where the wires are coming out of the wall. If the new mounting plate doesn't line up with the anchors used by the previous thermostat, make sure it is level and mark the holes where the new anchors need to be inserted. Use a cordless drill to make the necessary holes for these new anchors, and insert them flush with the wall. Pull the thermostat wires through the hole in the mounting plate and screw the mounting plate into place.

Step 4 – Attach the Wires and Install the New Thermostat

In most cases, the new thermostat should have terminals with lettering that corresponds with the older thermostat's connections. If it does, simply connect the wires to their designated terminals. However, if they don't match up, look in the instruction manual that came with your new thermostat for a wiring guide, and connect the wires accordingly. Snap the device into place on the mounting plate and insert the batteries (or vice-versa depending on the model).

Step 5 – Turn the Power Back On

Turn the breaker back on and switch your thermostat to AUTO. Set the temperature to a higher degree than what the current room temperature reads (or lower if you're testing an AC unit). In a few seconds, you should hear the air kick on. Then, follow the programming instructions that came with your device to customize your individual settings.

If your old thermostat featured a mercury tube, do not throw it into your regular trash! Be environmentally responsible and contact your local waste management authority to find out how to properly dispose of the unit.

Wayne McCarthy, plumbing and HVAC professional contributed to this article.