Look at your furnace/HVAC unit's control board and see if there is a "C" terminal. If so, then see which wire, if any, it's connected to. That is your "C" wire at the thermostat.
Honeywell (and others such as Trane) use a C wire on models that use WiFi or voice recognition or Z-wave so they can have a 24V connection.
Add an Adapter
Some smart thermostats include an adapter in case there's no C-wire in your home. You can also find thermostat adapters at a hardware store or online. If you have previous electrical experience, you can follow the instructions included with the adapter to install it.
The C, or common wire, provides smart thermostats with continual power. It's usually blue, but it may also be black, brown or purple. The O or orange wire connects to your heat pump (if applicable).
If there is no hidden C-wire, you can use a G-wire instead. However, you will not be able to use your fan independently when the heating or cooling isn't running.
The orange thermostat wire connects to your heat pump if you have one. It connects your thermostat to your outdoor condenser to reverse valve operations from hot to cold. The orange wire connects to terminal O on your thermostat. The orange wire only applies to homeowners who have an air-source heat pump.
Some models, such as Google Nest, are designed to work even if your home doesn't have a C-wire. * On the other end of the spectrum, many smart thermostats from Honeywell Home, Emerson, and ecobee do require a C-wire but may include an adapter kit as a workaround.
Nest thermostats are designed to use very little power, and in many cases they can use your system's heating and cooling wires to get enough consistent power. But sometimes, you may need to connect a common wire (C wire) or power accessory, like the Nest Power Connector, to make your system compatible.
Look in the wall behind your thermostat and see if perhaps there is an unused wire. If so, connect one end to C on your thermostat and the other end to C/Common on your furnace/air handler. Voila, you have C wire. 😁 Kill the power to your furnace first of course.
In many recently-constructed homes, the HVAC c-wire is already installed. However, in homes that are only a few years old or older, the wire may need to be installed as part of the new smart thermostat installation.
The most common configuration is five wires. However, you could see as few as two and many as ten. Make a note of any present wire not connected to a terminal. Do not label these wires.
This Honeywell programmable thermostat uses an internal disposable battery for its primary power. A "C" wire is not required. It will work with a 2 wire system.
You require a common wire (C wire - usually blue) to power on the unit since it does not take batteries. I think there is a workaround, but you need to call Honeywell support to make sure.
Typically, it will be on the inside of the access cover. In some cases, the wiring schematic may also be in the manual for the equipment which can be attached to the equipment. This can be used to locate the C terminal.
Look for connectors that have labels that are the same as your thermostat. For instance, you might find labels like R, W, G, Y, C or O/B. You should find wires attached to these connectors that are the same color as the wires that connect to your thermostat.
#1 Option – Do Nothing At All – The good news is that all smart thermostats don't require a C-wire. Some can work equally well without them. However, the claim is slightly misleading because, in these cases, the thermostat draws the necessary power for its screen and Wi-Fi capabilities by stealing power.
A C-wire, or a common wire, runs from your low-voltage heating system (24v) and carries continuous power to your thermostat. In today's electric market, most newer heating and cooling systems have C-wires, which guarantees compatibility for the installation of all smart thermostats.
The Honeywell Home T5 Smart Thermostat without C-Wire Adapter offers a range of features to enhance your home comfort and energy efficiency. With its auto home and away modes, this ENERGY STAR certified thermostat ensures your home is always at your preferred temperature while saving you money on energy bills.
In most homes, the common wire color is white. However, in some cases, it may be labeled or marked differently. Neutral Wire: Typically white or gray. Hot Wires: Black, red, or blue (depending on the configuration).
2 wire might be only R and Y for a cool only stat or R and W for a heat only. 4 wires would work for a furnace with an attached AC, with R, W, G, Y. R brings constant power in, and sends power out on G for the indoor fan, Y for cooling, and W for heating. If it's digital you'd need a battery in it.
Does red wire go to RC or RH? There is no standard for the color of the RH wire, but most units use a red one. The RC wire, on the other hand, refers to “red cooling”. It's the same with the RH wire in that it powers the thermostat.
Red and Orange Electrical Wires: Red and orange wires are secondary live wires, with red used in low-voltage applications and orange used as a high-voltage wire color.