CAUTION: Although replacing a thermostat does not appear to be a very technical task, it does involve proper wiring placement and technique. Before deciding to replace your own, please keep a few things ls in mind: If wires are misplaced or confused, if you do not possess a basic knowledge of electical fundamentals, or are unsure that this is a project for you, then please go no further. A mistake made in what seems to be an elementary task, can cost you a lot more in repairs than your original thermostat replacement. It may be in your best interest to have a qualified Service Technician perform this task for you.
There are many options of thermostats available, from expensive to downright cheap, highly sophisticated, multiple stage, heating, cooling, millivolt, heat pump, programmable, non-programmable, digital, analogue, and the list goes on.
The first step in installing a thermostat is choosing the correct one for your application. You will have to know what type of system you have in order to properly pick out and purchase one, no matter where you choose to buy it. Will your new thermostat be controlling a heating system, an air conditioner, or both? For this example we will say that you need a thermostat that will control a gas furnace with a central air split system installed in its ducting. Heating and cooling all-in-one. Now that you know what system you have, look at the packaging to verify the correct application and whether or not you want a programmable or non-programmable thermostat.
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You’ve now purchased the thermostat that matches your system and are ready to install it. It is important that at this step, you turn the breakers off to your heating and cooling systems. Inside the package you may find a set of decals labeled with a series of letters corresponding with the terminals of your new and old thermostat. These decals are to label the wires inside your old thermostat. Remove the old thermostat from its sub base. To do this you may have to loosen a few screws. Once you have the thermostat apart you will see were the wires fasten to it. Take each wire off one at a time labeling them as you go. Lets briefly familiarize you with the colors and terminal letters of the wires you are removing.
Start with the letter R: This is normally a red wire (color code is handy, but not always available). This is the 24 volt power wire coming from your furnace or air handler feeding power to the thermostat. On a heat and cool thermostat will have two: RC and RH.
RC is power for the cooling circuit and RH, power for the heating circuit. They will have a jumper across them if the heating and a/c are both controlled in the furnace. If they are separate units the jumper would be removed. Pay close attention to this as you label your wires.
C= This wire may be any color sometimes grey or brown. This wire is the common wire or 24 volts neutral. Your new thermostat may or may not have the terminal C. It would be used if your thermostat doesn’t require batteries or uses batteries as a back up.
W= This wire is normally white. It is your heating signal wire. The thermostat sends power from the R to W on a call for heat.
G= This wire is normally Green and is the signal wire for the fan relay of your furnace or air handler. The thermostat sends power from R to G on when the fan switch is turned on or a call for cooling.
Y= This wire is normally Yellow and is the signal wire for the cooling circuit. The thermostat sends power from R to Y on a call for cooling.
The letter terminals we have discussed are the basic wiring for a standard heat and cool system. There can be more terminals depending on what type of system you have in your home, such as heat pumps. Just be sure that if your thermostat has different letters, label them accordingly.
Your wires are labeled and you have removed the old sub base from the wall. Now you may fasten the new thermostat to the wall, using the screws and drywall anchors (if needed). Reattach the labeled wires to the corresponding lettered terminals, making sure you have good tight connections. For the system we are working on, we are connecting R,W,G,Y, and possibly C. The wires are connected and you attach the thermostat to its base. You’ve done it, the thermostat you have purchased has just been installed.
Now turn the breakers to your system on. The thermostat normally comes in the off position. You will run through the desired times and set point program in the manual provided with the new thermostat and set to your preferences. Turn the system on heat and test, making sure that the furnace comes on and shuts off. Then switch to cooling, set the proper temperature to make the air conditioning system come on. Verify that it too, comes on and shuts off.
There you have it
If you have any questions, please feel free to post them here.
I have included a video provided by Lowe’s for you to reference as a visual guide well. How To Install A Thermostat