How to Hook Up a Home Thermostat - If you need to install a new thermostat then you have found the right place to learn. Below we will describe to you how to hook up a digital thermostat, hook up a programmable thermostat, or hook up any type for that matter. Whether the old thermostat is bad or not if you simply want to replace your old one and hook up a new one the first thing you need to take into consideration is to select the right replacement thermostat. To select the correct replacement you need to know what kind of HVAC equipment you have in your home or where you want to hook up the new thermostat.  There are numerous types of air conditioner and heating combinations so in this article we will cover a basic gas furnace and air conditioner split system HVAC system. For hooking up a new thermostat similar systems to the air conditioner/gas furnace combination would be:

Related link: Thermostat Wiring Colors Code - Learn More about the Thermostat Installation (opens in a new window)

How to Hook Up a Home Thermostat

If you do not know what kind of unit you have take a look at the paperwork from the last time the unit was serviced. Perhaps it will show the type of equipment on the service ticket where the unit had maintenance.  It is assumed that most people will know what kind of unit they have so that they can select the proper thermostat.

How to Hook Up a Home Thermostat

  • air conditioner/oil furnace combination (4 to 5 wires)
  • air conditioner (stand alone with no heat source) (2 to 4 wires)
  • air conditioner with electric heat combination (4 to 5 wires)
  • Stand-alone gas furnace (2 to 4 wires)
  • Stand-alone electric furnace (2 to 4 wires)
  • Stand alone oil furnace (2 to 4 wires)

*It is possible to have more wires than noted here depending on the complexity of the system. This article assumes you have a basic single stage air conditioner/single stage gas furnace system.

How to Hook Up a Home Thermostat – Location of New Thermostat Installation

Now that you have selected the proper thermostat you want to install the new thermostat in place of the old thermostat. It is best to place the thermostat in the same location as the old thermostat.

Moving the thermostat to a new location is not recommended unless you hire an HVAC professional to relocate the thermostat first. Thermostats need to be located in a strategic area of the home to be effective and work properly. Besides you would have to pull new thermostat wire through the wall to relocate the thermostat and that is a big job for anyone.

Tools Needed – How to Hook Up a Home Thermostat

You will need a small flat head screwdriver, possibly a Phillips head screwdriver, a pair of electrical stripping and cutting pliers for #18 thermostat wire, a pen and paper, and some small labels to label the existing wires hooked to the existing thermostat. A small drop cloth or paper can also be used to place on the floor below the thermostat to catch dust, debris, and other stuff that can fall on the floor.

Step by Step – How to Hook Up a Home Thermostat

  1. Turn off the power to the air conditioner or furnace preferably at the electrical panel where the circuit breakers are located. For most split systems you will have two circuit breakers for the air conditioning and heating system. Make sure you flip both of these breakers to the off position.
  2. Remove the old thermostat – sometimes the old thermostat will have screws holding it to the sub-base and other times it will not have screws but with a little force will pop right off from the sub-base. If you do not see any screws give the thermostat a little tug and it should pop right off. If you have the original instructions for the old thermostat take a quick look at the installation instructions to how the old thermostat disassembles. Be careful hot to pull the sub-base from the wall when taking the thermostat apart. Once you get the thermostat separated from the sub-base go to the next step of hooking up a thermostat.
  3. Now that you have the main thermostat separated from the sub-base you will see the wires hooked up to the terminals on the thermostat. You can reference the thermostat color code chart to see what the thermostat wires are for, what the thermostat wires control, and to give you an idea of how to hook up the new thermostat. Take the piece of paper and pen or pencil and write down where each thermostat wire is landed on the terminal board. Then take the labels and label each wire for the terminal where the thermostat wire was landed and note the color to the terminal for the wires you will soon disconnect. Again, before touching any wires make sure the power is off. For the standard basic air conditioner/gas furnace combination you should have either 4 or 5 wires.* Red wire to red on the thermostat  terminal strip (this can also be an RC – RH terminal with a jumper between the two terminals) , yellow wire to Y on the thermostat terminal strip for air conditioning, white wire to the thermostat terminal strip for the gas furnace, a green wire to the G on the thermostat terminal board for manual blower fan operation, and an optional blue wire hooked to the common terminal or C terminal on thermostat terminal board.
  4. Now after making sure the power is off and you have written down where the thermostat wires go and have labeled them you can disconnect the wires from the old thermostat and remove the old sub-base from the wall. Be careful not to let the wire fall into the wall. You can use a pen or pencil and wrap one of the wires around the pen or pencil so the thermostat wire will not slip and fall into the hole in the wall.
  5. Mount the new thermostat sub-base using the same holes the old thermostat sub-base was mounted to and tighten it down until it is secure. The old holes should match up to the holes in the new thermostat sub-base so you will likely not need any new screws or anchors.
  6. Attached the thermostat wires to the designated terminals as noted in your notes and how the wires are labeled. This should be cut and dry as the old thermostat terminals should match up to the new thermostat terminal connections. See the installation guide that came with the new thermostat for further instructions if anything is different.
  7. Next, install the new thermostat onto the sub-base as per manufacturer instructions. A little care may be taken here to make sure the pins line up from the sub-base to the thermostat base as the pins can easily be bent if not properly aligned.
  8. Restore power and test the system for proper operation. A proper test would include testing the furnace for heating, testing the air conditioner for cooling, and testing the fan for manual operation. Make sure each unit cycles on and off as usual taking into account there are built in time delays possible in both the thermostat and the HVAC system. If something doesn’t start right away don’t freak out as most systems have time delays to protect the equipment.
Related Link: Running New Thermostat Wire - Learn Tips and Tricks to Running New Thermostat Wire (opens in a new window)

How to Hook Up a Home Thermostat - Conclusion

High Performance HVAC hopes this “How to Hook Up a Thermostat” article helps you when you have to hook up a new thermostat. See our other articles about thermostat installation and don’t forget to book mark us and give a nod or two with Facebook and the Google Plus One button.

See a video about the common mistakes when hooking up a new thermostat.

Mistakes Made When Hooking Up a Thermostat Video

Find more about thermostats here.

High Performance HVAC
How to Hook Up a Thermostat

share arrow hvac

It seems like you are going to leave us. First of all, we don't want you to go but if you do please share our site before you go! It only takes a minute...........and most of all we sincerely appreciate it!! Consequently, we promise our plans only include helping others and not world domination (-:

share arrow hvac

Pin It on Pinterest

Shares