Principles of Ductwork Design

The principles of good ductwork design are more important than ever. With energy costs climbing, what was once considered the status quo in residential ductwork is no longer acceptable. Ducts must be designed and individually sized to the heating and cooling requirements of each home, using industry standard formulas and software such as the Air Conditioning Contractors of America Manual J, S and D. In addition to these critical calculations, a number of general principles of duct design guide the process, whether in new construction or a home HVAC renovation.

• Wherever possible, ducts should be routed through conditioned areas of the house. Unconditioned zones such as the attic, crawl space, or the voids inside exterior walls expose ducts to excessive thermal loss or gain, making a furnace or A/C run longer and raising operating costs.
• All joints between spans of ductwork should be sealed with mastic and metal tape, then secured with sheet metal screws. Ductwork insulated to a level of R-8 should be utilized wherever ducts are affected by acute temperatures. After installation, ducts should be pressure-tested to verify that leakage is within allowable limits as prescribed by local codes.
• Design as few curves, bends and right angles as possible into the system. Also minimize the number of joints or transitions. All such deviations impose friction to the passage of air inside the ducts, reducing airflow. Locate the system air handler as centrally as possible to all rooms in the house in order to reduce the total length of the duct system.
• Ideally, each room in the house with a supply air vent should also have its own dedicated return air vent. Where this isn’t feasible, a central return should be located in a hallway or other common area. Ensure that the air path from individual rooms back to the central return is always clear by utilizing air pass-through grates installed in doorways or jumper vents between rooms.

Contact Energy 1 Heating & Air Conditioning for more about optimizing ductwork design for heating and cooling efficiency and comfort.

Our goal is to help educate our customers in Lorain, Ohio about energy and home comfort issues (specific to HVAC systems). For more information about ductwork design and other HVAC topics, download our free Home Comfort Guide or call us at 440-201-2959.

Credit/Copyright Attribution: “Boobl/Shutterstock”