Installation

Adding a 24 VAC external transformer: A DIY option for heat-only systems without a common wire

If you have a heat-only system connected to your Sensi thermostat, an easy option for adding a common, or c-wire, is to install a 24 VAC wall plug-in transformer. Transformers with 150-400mA output are the most widely available online and easily provide sufficient power for the thermostat. Please note the wires from the wall plug-in transformer will be visible unless installed behind the wall.

If you purchase a transformer that is used to charge or power electronic devices, you will need to cut off the accessory plug (located at the end of the cord, opposite of the outlet plug) and split the two wires apart. Strip the cord around the two wires to expose a small amount of the copper wiring inside, which will be inserted into terminals on the Sensi thermostat base.

Insert one wire into the unused “R” terminal on the thermostat (RC or RH) and the other wire into the “C” terminal. Make sure to cut the red RC/RH jumper on the back of the Sensi face plate. Finally, plug the adapter into a nearby wall outlet. Note: Wire colors from the system may vary.

Sensi Smart Thermostat - jumper wire

Sensi Touch Smart Thermostat - jumper wire

*Note: This is not an option for cool-only systems or combined heat and cool systems.