📋 How to Add a C-Wire to a Smart Thermostat (Without Rewiring)

Follow these steps in order. Takes about 5–10 minutes from start to finish.

• Step 1: Turn off power to your HVAC system at the breaker. Remove the thermostat and check the existing wiring — look for a blue or black wire not connected to any terminal.
• Step 2: If you have an unused wire in the bundle: connect it to the C terminal at the thermostat and the C terminal on the HVAC air handler control board. This is the cleanest solution.
• Step 3: If no spare wire exists, use the Nest Power Connector ($10): plug it into the air handler control board terminals and run the included 2-wire cable to the thermostat. Solves C-wire without any new wiring.
• Step 4: For Ecobee: use the included PEK (Power Extender Kit). It plugs inside the air handler and provides a 24V common connection via your existing 4 wires.
• Step 5: For universal C-wire adapters: connect the adapter to the air handler board and run a new 2-wire cable to the thermostat C terminal. Available on Amazon for ~$15.
• Step 6: Turn power back on and verify: in the Nest app go to Settings → Technical Info → Power. Vin should read 24-30V. In Ecobee go to About and check for a C-wire tick.