Tag Archives: run new thermostat wire

Re-wiring to add a C-wire? Read this!

If you’re re-wiring to get a C-wire, pull new thermostat wire with at least 7 or 8 conductors.

Running completely new thermostat wire to get a C-wire is a great way to upgrade your home’s wiring and add some future-proofing. If you’re going to go through all the hassle of pulling out the new wires and threading new ones through your walls and floors, do everyone a favor and choose a new thermostat wire bundle with at least 7 or 8 conductors. Conductors are the little colored wires inside the thermostat wire bundle. The more you have, the more things you can hook up now or in the future. 

Things you (or your home’s future owners) might want to add to your HVAC setup include:

  •  heat pump 
  • dehumidifier
  • multi-stage furnace 
  • air conditioner
  • individual fan control 
  • smart thermostat that requires a c-wire

How to tell how many conductors are in a bundle of thermostat wire

The number of conductors in a bundle of thermostat wire are indicated by the second number in a fraction that looks like this:

  • 18/3 – 3 conductors inside this wire
  • 18/5 – 5 conductors inside this wire
  • 18/7 – 7 conductors inside this wire


It’s fine to run more conductors than you need right now. Tuck the extras into the wall behind the thermostat, and simply leave them unhooked up in the furnace.

Where to buy thermostat wire

It might not be easy to find this many conductors or in a length under 250 feet if you’re shopping locally, so look online for your new thermostat wire. We recommend shopping on Amazon.com for thermostat wires. Amazon offers a greater variety of conductors and lengths, as well as fast shipping and easy returns.