Based on the thermostat model, you may need the "C-Wire" (Common Wire).
System | Sensi Lite | Sensi Smart | Sensi Touch | Sensi Touch 2 |
| | | | |
Heat Only | Yes (3) | Yes (3) | Yes (3) | Yes (3) |
Cool Only (AC) | Yes (3) | Yes (3) | Yes (3) | Yes (3) |
Conventional Heating & Cooling | Yes (1) | Yes (2) | Yes (3) | Yes (3) |
Heat Pump/ Geothermal | Yes (1,3) | Yes (3) | Yes (3) | Yes (3) |
Humidifiers/Dehumidifiers | No | Yes | Yes | Yes |
Communication/ Proprietary System | No | No | No | No |
Millivolt | No | No | No | No |
Line Voltage | No | No | No | No |
RV/ Camper Applications | No | No | No | No |
Conventional Heating and Cooling Systems
- Gas/Oil/Propane Furnace
- Boiler/Radiant
- Air Conditioner
- Electric Furnace
Heat Only Systems:
- Electric Furnace
- Boiler/Radiant
- Gas/Oil/Propane Furnace
- 1- Compatible with multi-stage systems up to 1H/2C or 2H/1C
- 2- "C-Wire" required for HomeKit compatibility
- 3- "C-Wire" required

Incompatible Systems:
- Communication/ Proprietary System
- Line Voltage Systems (generally 110V/220V baseboard heating)
- 12VDC (RV/campers) Applications
- Stranded Wiring
See the article in the link
here for more information on Emerson Sensi thermostats
Learn more on HVAC systems and controls in the link
here.
Contact our HVAC Controls Engineering team for assistance with custom HVAC control solutions.