C-Wire: Everything You Need to Know | Honeywell Home
If you are installing a new thermostat, but your current one is missing a c-wire, you have the following options:
- check if there is an unused c cable
- use a c cable adapter
- check if your system is heat only or redlink
check for unused c-wires
some houses have an unused c cable hidden in the wall. to check for an unused c wire:
-
turn off power
To protect your equipment, turn off the power at the breaker box or switch that controls your heating and cooling equipment.
note: the thermostat’s off switch will not turn off the equipment.
check that your system is off
Change the temperature on your existing thermostat so your system starts heating or cooling. If you don’t hear or feel the system turn on within 5 minutes, the power is off.
Note: If you have a digital thermostat that has a blank screen, skip this step.
On most thermostats, you can remove the thermostat by gently grasping and pulling. some thermostats may have screws, buttons, or snaps.
note: do not remove any wires from your thermostat at this time.
do you have a line voltage system?
Line voltage systems have thick black wires with wire nuts or are labeled high voltage (120v or higher).
yes, your system may not be supported. contact support at 1-855-733-5465 to find a professional installer in your area.
no, continue to the next step.
take a photo of your existing wall plate wiring
make sure you have a good view of all terminals. you may need to refer to this image later.
A jumper is used to connect two terminals. it may look like a small staple or colored wire.
note: do not discard any bridges.
label wires
Label each wire on your existing wall plate with the stickers provided with your new thermostat. if you don’t have stickers, you can use tape and a pen.
note: do not tag the jumpers.
note the colors of the wires
Check the boxes and note the color of the wires connected to the terminals on the existing wall plate. check all that apply (not all will apply).
Note: If there are wires on terminals that are not listed, you will need additional wiring support. contact support at 1-855-733-5465.
disconnect wires and remove existing wall plate
Some wire terminals are “push” type (gently press down on the terminal to release the wire) and some are flat head screws. you may need a screwdriver to free the wires from the terminals.
note: wrap the wires around a pencil to prevent them from falling into the wall.
do you have a c-wire?
this is to confirm that your system is not using a cable c. look at the thermostat wiring checklist in step 8: was terminal c checked? Alternatively, you can look at the photo in step 5: Is there a wire on the c terminal?
yes, this means your thermostat is using a c-wire and you don’t need to install a c-wire adapter. you can continue installing your new thermostat.
no, this means your thermostat is not using a c wire. continue to the next step.
Go to your furnace or heating systemThis system is typically located in your basement, attic, or garage.
Do you have a zoning panel?
Your zoning panel is often mounted to your furnace ductwork. It usually has one bundle of wires that connect to your heating/cooling system, and smaller bundles of wires that connect to the duct dampers.
yes, c-wire adapter installation is more complicated for zoned systems. contact support at 1-855-733-5465 to find a professional installer in your area.
no, continue to the next step.
return to your current thermostat
Do you have an unused cable?
You previously removed the existing wall plate. look at the bunch of wires sticking out of the wall.
note: you may have to pull the bundle of wires out of the wall to find the unused wire.
yes you can use this unused c cable. continue with step 13.
no, since it doesn’t have a c cable, you need to use a c cable adapter. continue to the c-cable adapter usage section.
tag unused wires
Label your unused wire with the “c” label provided with your new thermostat. If you don’t have stickers, you can use tape and a pen. you may need to use a wire stripper to expose at least 1/4 inch of wire.
Note: If you have multiple unused cables, label only one cable and make a note of the color.
Go to your furnace or heating systemThis system is usually located in your basement, attic, or garage. bring a flashlight and a screwdriver.
remove the lid of the oven or heating system
open the cover of the heating and cooling system to find the control board. the control board can be at the top or bottom. you should see the same terminal labels that are on your thermostat.
Note: If you don’t see a control board, your system may not be supported. contact support at 1-855-733-5465 to find a professional installer.
In step 12, you found a bunch of wires near your existing thermostat. Locate the other end of this pack near your furnace or heating system, then find the unused cord.
Note: The unused wire should be the same color as the one near your current thermostat. see step 13 to see the color you wrote down.
connect unused wire to terminal c on control board
note: if there are existing wires on terminal c, make sure they are still connected after connecting the unused wire.
close the lid of the oven or heating system
make sure the cover is completely closed. some systems will not turn on if the cover is not completely closed.
Congratulations, you have connected an unused c-wire! you won’t need to use a cable adapter c. now you are complete.
use c-wire adapter
a c cable adapter replaces the need for a c cable. the c-wire adapter is included in newer honeywell wireless thermostats. If you have an older thermostat model, you can purchase a c-wire adapter here.
to use a c: cable adapter
In step 7, you labeled the wires on your existing wall plate. look at those wires and make sure you have both a g and y labeled.
yes, this means your system is compatible with the c-wire adapter. continue to the next step.
no, your system does not support the c-wire adapter. contact support at 1-855-733-5465 to find a professional installer.
change the label of your g cable to “c”
Relabel your wire g with the label “c” provided with your new thermostat. if you don’t have stickers, you can use tape and a pen.
Relabel your wire y with the “k” label provided with your new thermostat. if you don’t have stickers, you can use tape and a pen.
Go to your furnace or heating systemThis system is usually located in your basement, attic, or garage. bring a flashlight, tags, phone, and screwdriver.
remove the lid of the oven or heating system
open the cover of the heating and cooling system to find the control board. you should see the same terminal labels that are on your thermostat.
note: you may need to unscrew the cover. the dashboard can be at the top or bottom.
take a picture of the control panel wiring
make sure you get a good view of the following terminals, as you may need to reference this image later:
- g
- c
- r
- w or w1 (not on all systems)
- y or y1
note: if you have wires connected to two r terminals, then you have a two transformer system and need additional assistance. contact support at 1-855-733-5465 to find a professional installer.
label wires
Label each of the following wires with the stickers provided with your new thermostat:
- g
- c
- r
- w or w1 (not on all systems)
- y or y1
If you don’t have any stickers, you can use tape and a pen.
note: if there are multiple wires connected to one terminal, only label the wires going to your thermostat *.
disconnect the labeled cables
Disconnect only the wires you labeled. do not disconnect any untagged wires. if unlabeled wires become disconnected, reconnect them immediately.
note: you may need a screwdriver to release the wires from the terminals.
connect the labeled cables to the c cable adapter
on the “thermostat” side of the c-wire adapter, press a tab to open the corresponding terminal. insert the labeled wires into the following terminals:
- w-wire -> terminal w
- wire g -> terminal c
- wire and -> terminal k
- wire r -> terminal-r
note: this will convert g to c and y to k.
make sure the cables are connected
pull gently on the cables to make sure they are connected to the c-cable adapter.
connect the c-wire adapter to the control board
on the “equipment” side of the c-wire adapter, connect the wires to the corresponding terminals on the control board.
note: be sure to remove the plastic tip from each wire before connecting it to a terminal.
c mount cable adapter
Use the included bracket and adhesive pad to attach the c-cord adapter inside your furnace or heating system.
note: make sure your cables are not overstretched or strained.
close the lid of the oven or heating system
make sure the cover is completely closed. some systems will not turn on if the cover is not completely closed.
Congratulations, you have connected a c-cable adapter! now you are complete.
check if your system is heat only or redlink
Both heat only and red link thermostat systems have only two wires, typically r and w for heat only systems. Heat Only and RedLink 2-Wire Only thermostats are not directly compatible with Wi-Fi thermostat replacements or C-Wire adapters. contact support at 1-855-733-5465 to find a professional installer.
turn off the power
To protect your equipment, turn off the power at the breaker box or switch that controls your furnace or heating equipment.
note: turning off the thermostat will not cut power to the furnace or heating equipment.
Change the temperature on your existing thermostat so your system starts heating or cooling. If you don’t hear or feel the system turn on within 5 minutes, the power is off.
Note: If you have a digital thermostat that has a blank screen, skip this step.
On most thermostats, you can remove the thermostat by gently grasping and pulling. some thermostats may have screws, buttons, or snaps.
note: do not remove any wires from your thermostat at this time.
check how many wires you see connected to the terminals.
yes, continue to the next step.
no, it does not have a heat only system.
Are the 2 wires connected to the r and w terminals?
yes, it has a heat only system, which is more complicated. contact support at 1-855-733-5465 to find a professional installer in your area.
no, you may have a red link system, which is more complicated. contact support at 1-855-733-5465 to find a professional installer in your area.
