This Air Distribution System Design: Good Duct Design Increases Efficiency (PDF) fact sheet explains how good duct design increases efficiency of air distribution systems for central heating and cooling. The air distribution system may reach an efficiency of 80 percent or more for little or no additional cost, resulting in homeowner savings of $50 to $200 or more each year in heating and cooling costs. The fact sheet describes duct design objectives, types of supply duct systems (such as trunk and branch, spider, radial and perimeter loop systems) as well as return duct systems (including multiple-room return and central return systems), duct materials and duct and register locations. It also provides duct design methods, design recommendations and key design elements.
U.S. Department of Energy - Energy Efficiency and Renewable Energy