Stackable thermostat

A method for installing a thermostat where fewer pre-installed thermostat wires are available to an installer than are needed for connecting the thermostat to an HVAC plant comprising steps of:

• providing pre-installed thermostat wires;
• providing a thermostat having two separable sections, the thermostat including a user interface module and an I/O module;
• locating the I/O module physically near the HVAC plant;
• connecting a plurality of wires between the I/O module and the HVAC plant to control the HVAC plant with the I/O module;
• locating the user interface module in a space where comfort levels are to be controlled by the thermostat;
• and
• connecting the user interface module to the I/O module using pre-installed thermostat wires to facilitate communications and electrical power transfer between the user interface module and the I/O module,
• wherein the number of pre-installed wires is less than the number of wires that are used to electrically couple the I/O module to the HVAC plant,
• wherein the thermostat can be mounted and operated in one of two user selectable installations selected from at least one of:
• a stacked configuration that comprises a thermostat, which has the user interface module directly mounted to the I/O module, and
• a remote configuration that comprises a thermostat, which has the user interface module remotely mounted from the I/O module,
• wherein in the remote configuration the I/O module is located in a first space that houses the HVAC plant,
• wherein the user interface module is located in a second space where comfort settings are maintained, and
• wherein the first space is different from the second space.