Honeywell thermostats with three wires labeled 123 are generally associated with basic heating-only systems. These thermostats are typically used for controlling a single-stage heating system, such as a furnace or a boiler.
The wiring configuration is straightforward:
- The "1" wire (sometimes labeled "W" or "W1") is for the heating call and connects to the "W" terminal on the thermostat.
- The "2" wire (sometimes labeled "R" or "Rh") is for the power supply and connects to the "R" or "Rh" terminal.
- The "3" wire (sometimes labeled "C") is the common wire and provides 24-volt power to the thermostat. It connects to the "C" terminal if the thermostat requires a common connection for power. If the thermostat doesn't have a "C" terminal, you may not need this wire for basic heating-only systems.
It's important to note that the labeling and color-coding of thermostat wires can vary, so always refer to the user manual or the specific wiring diagram provided by Honeywell for your thermostat model.
Keep in mind that thermostats and HVAC systems can differ, and some Honeywell thermostats may have more advanced features, such as cooling control or compatibility with multi-stage heating and cooling systems. If you're unsure about the wiring or compatibility of your thermostat, it's best to consult a professional HVAC technician to ensure proper installation and operation.