Windshield deicing performance is a key metric for HVAC system development and optimization within the sphere of commercial vehicle design. The primary physical properties that drive this metric are pressure drops in the HVAC ducting, flow rate of the air through the system, and the transient warm up curve of the HVAC unit. However, many design engineers also have to take underhood packaging into consideration while trying to optimize a new HVAC system design. This study leverages historical deicing simulation methodologies in conjunction with modern computational horsepower so as to optimize the HVAC ductwork in the studied commercial truck at the front end of the design process. By iterating on a design in the computational domain under steady-state and transient flow and thermal conditions, a robust HVAC system design can be created even prior to the prototyping stage of development. Furthermore, when the vehicle runs through an experimental regime, the design engineer has reasonable certainty of meeting their targets with respect to the HVAC system’s deicing performance. By completing steady state cold flow and transient deicing simulations, one is able to better identify key duct design parameters that can improve deicing performance. Using CFD, the design engineer is better equipped to make informed design decisions in a shorter duration of time.