Article Summary:
Some heating and cooling systems use their own proprietary communication protocols instead of commonly accepted standards. The Nest Learning Thermostat isn’t compatible with these systems.
Most thermostat wires are simple on-off switches. When wires are shorted to the power wire (R), a simple electrical signal is sent to the heating and cooling equipment. This is how the vast majority of low voltage systems work.
However, proprietary systems use a serial communications protocol to communicate across the wires between the system and the thermostat. These protocols are specific to the manufacturer of the system--they aren’t standardized across the industry. This means that only thermostats made by the same manufacturer are compatible with these proprietary systems. A benefit to making systems proprietary is that fewer wires can be used to control the system. For this reason, many system manufacturer’s high-end and multi-stage brands are proprietary--such as the Carrier Infinity and Bryant Evolution lines.
Some proprietary systems also have the option to use standard heating and cooling wires. In this case, a professional may be able to rewire your system to work with the Nest Learning Thermostat. If you think your system may use a proprietary communications protocol, you should contact a Nest Pro installer in your area for help.