Nest is designed to be compatible with low voltage, 24 volt systems. Nest is not compatible with millivolt or high voltage (line voltage) systems.
Nest works with low voltage, 24 volt systems with a tolerance of +/- 15%. Each wire that Nest uses to draw power (C, Y1, and/or W1, depending on the system) must comply with these voltage requirements.
| Power Wire Connections | Positive Power Terminal | Negative Power Terminal | Voltage Requirement |
| C Wire Connected | Rc (Rh if Rc is not connected) | C | 24V +/-15% |
| Y1 Wire Connected, C Wire Not Connected | Rc (Rh if Rc is not connected) | Y1 | 24V +/-15% |
| W1 Wire Connected, C & Y1 Wire Not Connected | Rc (Rh if Rc is not connected) | W1 | 24V +/-15% |
Some HVAC systems have high resistance in series with the Y1 and/or W1 power lines. This can prevent the voltage requirement from being met during Nest Learning Thermostat operation. In order for the Nest Learning Thermostat to be compatible with these systems, a common (C) wire is required.
For more information, please see:
Related to...
- Nest Learning Thermostat