How do you hook up the nest thermostat
wiring - Where do I connect the C wire in my furnace? - Home Improvement Stack Exchange
Central heating and air conditioning HVAC systems are all controlled by some kind of wall-mounted thermostats that sense room temperature and turn the systems on and off whenever necessary. There are quite a number of different thermostat styles, ranging from the old standard mercury-contact thermostat in the familiar Honeywell dial style, to extremely modern digital thermostats that operate entirely by touch-screen controls. When an existing thermostat goes bad, it's a fairly easy matter to replace it. Most new thermostats come with directions for how to adapt the device for different systems—and this is fortunate, because an HVAC system may use as few as two wires or as many as four or more, depending on how many components there that need to be controlled. For example, if the thermostat operates only a boiler, there may be only two low-voltage wires to connect, while a thermostat that controls a forced-air furnace, central air conditioner, and a heat-exchange filter, may have as many as five wires. Many modern thermostats will work for simple as well as complex systems—it's just a matter of how many wire connections you'll need to make.
How to Attach Wiring of Your Heater Thermostat to Your Furnace
While there isn't an official standard for thermostat circuit wiring colors, there is a general pattern. Your best bet is to see the manufacturer's documentation both thermostat and HVAC. If there is a short then the current through the tiny wires could cause a fire Thermostat wires are usually 18 gauge. These colors are not standard for thermostats. If you need an inexpensive meter to work with thermostat wiring see M
Your furnace thermostat is an essential part of a home furnace system. The thermostat is responsible for regulating the other systems inside the furnace; it is primarily in charge of maintaining temperature. If the thermostat is not working properly, you may find that your home is colder or warmer than you would like it to be. Your electric bill may also shock you, as the furnace may be overworked.