Making the decision to replace an old-fashioned thermostat with a newer, programmable model is one of the most effective ways to control your heating and cooling costs. Luckily, it’s a relatively easy job for the casual do-it-yourselfer who is looking for easy AC maintenance tasks they can do themselves.

But, before you head over to the home improvement store and pick a new thermostat, you need to make sure the one you pick will work with your home’s system.

Depending on your home’s HVAC system, your existing thermostat could be powered by anything from 8-volts to 24-volts, so you need to learn what your system uses so you can buy the correct thermostat the first time. To learn this information, remove the existing thermostat and look for the information on its interior label.

Replacing a Thermostat

Tools and Materials

  • Screwdrivers
  • Torpedo level
  • Pencil
  • Pen
  • Masking tape
  • Utility knife
  • Needle-nose pliers
  • New thermostat

Step 1: Remove the Old Thermostat

Depending on the age of your existing thermostat, the wires may be attached to the front end, or they may be connected to the mounting bracket. For this reason, use care when prying the face plate off of the thermostat.

Before you disconnect the wires, place a piece of masking tape on each one and use the pen to mark the tape with the letter that corresponds with the terminal to which each wire is connected. This will help you determine where you need to connect them on the new thermostat.

If the wires are attached to the thermostat’s front half, disconnect them now and set the thermostat aside.

Since thermostat wire runs straight out of the wall and doesn’t use a wall box, wrap the wires around a pencil to prevent the thin cable from slipping back into the wall.

Remove the screws that secure the mounting plate to the wall and remove the plate.

Step 2: Install the New Mounting Plate

Slip the wires through the hole on the backside of the mounting bracket and align the bracket where you want to install it. If the previous thermostat’s anchors do not match the mounting holes on this plate, you will have to mark their locations and install wall anchors. Before you make your marks and secure it to the wall, make sure the mounting plate is level by placing a torpedo level along the top of it.

Step 3: Check the Wires for Damage

Thermostat wires are very thin and can break easily. Before you make your new connections, inspect the wires to make sure they are all in good condition. If any show signs of damage or corrosion, cut away the bad portion of wire and re-strip a fresh lead using the utility knife’s edge.

Step 4: Wiring the New Thermostat

On the back of the thermostat, or on the mounting plate, you will see a series of screw terminals. Each terminal has a corresponding letter assigned to it. Look at the letter you labeled on each wire and connect it to the matching terminal on the new thermostat. If you come across a letter that is different, refer to the manufacturer’s instruction paperwork to see which terminal you should use for that given wire.

Step 5: Finishing the Installation

Snap the new thermostat on to the mounting plate and insert the included AA battery (or batteries) into its chamber. For programming instructions, refer to the manufacturer’s paperwork included in the packaging.

You may also like

2 Response Comments

  • ariel mercado  December 7, 2015 at 7:07 pm

    I have a mercury thermosate that works with a gas steam radiator. and im wondering how can i get another one i try using the replacement thermostat murcry free but it does not work only the murcury one work please let me know thanks

    • DRKMTTR  July 1, 2016 at 12:38 pm

      Wondering how this turned out. Did you make sure the wiring was correct? Also, did you make sure to recycle the thermostat? Depending on the state you live in, it might be the law!

Leave A Comment

Please enter your name. Please enter an valid email address. Please enter a message.