I Want a Smart Thermostat but Don't Have a C Wire - What Are My Options?

June 09, 2021

When you’re seeking approaches to reduce heating and cooling bills, installing a smart thermostat is a smart decision. These devices learn the temperatures you like and routine and then make an energy-efficient schedule that matches. What’s even better is that you can change and keep an eye on your settings from just about anywhere with your phone, whether you’re lying in bed or on the go. (You might even be able to get a free smart thermostat depending on rebate programs from your utility company in Florissant.)

Most of the time, hooking up a smart home thermostat with the support of B & B Heating & Cooling is an uncomplicated task if you have a more modern home. But what if your home is older or doesn’t have the correct wiring? Can you still add a smart thermostat without C wire? We’ll help you figure out the process so you can pick the proper thermostat and enjoy energy savings for years to come.

What Is a C Wire and What Does It Do on a Thermostat?

Many programmable thermostats need batteries. When you’re switching to a smart thermostat, you’ll find that many need a C wire, or common wire, for power. Without this wire, your new thermostat could cause your heating and cooling system to have glitches.

You can determine if you have a C wire by doing the following:

  1. Switch off power to the thermostat at the breaker.
  2. Remove the thermostat and look at the wiring.
  3. If there are five or six multicolored wires, you have what’s needed for a smart thermostat. You might be wondering what color is the C wire on a thermostat—and the answer to that is often blue.
  4. If there are three or four thin multicolored wires, you’re almost there. Make sure the C wire isn’t tucked inside the wall. If you can’t find one, we may be able to put in one for you or you may be able to use your new thermostat without one.
  5. If you have two thick wires, you may be able to use a smart thermostat with an adaptor designed for high-voltage systems. Or you may be able to use a battery-powered smart thermostat, like the Lux Geo Wi-Fi Thermostat, if your wiring is incompatible and you don’t want to put in new wiring.

Do Nest or ecobee Need a C Wire?

Two of the most popular brands are the Nest smart thermostat and ecobee smart thermostat. If you have two to four wires, these thermostats may work for your needs.

Nest says its thermostats are designed to run on not a lot of power and can typically share it with your HVAC system. However, you may need to have a pro like B & B Heating & Cooling install a C wire with the Nest Thermostat E or Nest Learning Thermostat if you’re having power problems or a battery that’s constantly drained.

ecobee works with 24-volt systems (ones with three to six thermostat wires) and comes with a C wire adaptor. So, you’re taken care of if you don’t have a thermostat C wire.

Depend on B & B Heating & Cooling for Your Smart Thermostat Installation Needs

At B & B Heating & Cooling, we’re always looking for methods to keep you comfier while keeping energy bills reasonable. If you have questions about installing a smart thermostat without a C wire, contact us at 314-325-7552. We can help you pick the right model for your home and even add new wiring if required.