What system types is the TH8320U thermostat compatible with?

The TH8320U is compatible with gas, oil, or electric heat with air conditioning, heat-only two-wire systems, power to open and close zone valves, normally open zone valves, warm air, hot water, high-efficiency furnaces, heat pumps, steam, gravity systems, heat only with fan, cool only, and 750 mV heating systems. This makes it suitable for a wide range of HVAC configurations.