A climate control system may include a heating, ventilation, and air conditioning (HVAC) system for an indoor building area. The climate control system may also include a home automation (HA) thermostat device in the indoor building area. The HA thermostat device may include a housing, an indoor temperature sensor carried by the housing to sense an indoor temperature of the indoor building area, and a temperature controller carried by the housing. The temperature controller may obtain a setpoint temperature for the indoor building area, obtain an external temperature from the external to indoor building area, and determine a crossing of the external temperature of the setpoint temperature. The HA temperature controller may also switch the HVAC system between operating modes for heating and cooling based upon the crossing of the external temperature of the setpoint temperature and the indoor temperature moving beyond the setpoint temperature by a threshold temperature difference.
