Choosing the right-sized duct is critical to maintain proper air flow in the system. Pictured is a simple model for routing ducts. Because of the complexity of designing duct systems, It’s Phenomenal Air Heating and Cooling highly recommends using the ACCA “Manual D” for sizing ductwork, or consulting a professional HVAC contractor. For all of your HVAC Air Flow Design needs, Call It’s Phenomenal Air Heating and Cooling.