A system and method for managing power consumption of HVAC system includes a transfer switch, a detector interface and an HVAC controller of the HVAC system. The transfer switch is configured to switch a power line supplied to a load between a utility power source and a backup power source. The detector interface is in communication with the transfer switch or a controller of the backup power source and the HVAC controller. The HVAC controller is configured to receive data regarding the switching of power line supplied to the load between the utility power source and the backup power source and control an operation of components of the HVAC system based on the capacity of power source, thereby manages or lowers the power consumption of HVAC system. The detector interface is configured to provide switching information and capacity of the backup power source to the HVAC controller.