Proper Basement Ductwork

Use Straight Lines

• The best basement duct system uses as many straight lines as possible in a "trunk and branch" design with a central main supply duct and smaller forks off to individual vents. Vents run along outside walls, usually under windows, with the main line ideally running down the center of the basement. Vents extend through the floor into the basement so a connection forms from the bottom.

Balance

• A heating/cooling system needs to be balanced, with return ducts taking "used" air from inside the house back to the unit. The return entry points will be in a central area, such as a hallway where air flows naturally, with a filter system in the house and an opening in the floor into the basement. Return ducts generally are larger because one or two ducts must handle all the airflow of all the supply ducts. If possible, route return ducts alongside the main supply duct.

Joists or "Natural" Supports

• Basement ductwork gets routed between or along floor joists and fastened to wooden joists with metal hangers and nails. It may use "natural" supports like gas lines and braces between joists. In addition to supplying floor vents in the house, a basement system may connect ceiling vents in the basement.

Use a Floor Plan

• The best way to design basement ductwork is with a floor plan, which shows the location of the heating/cooling unit, all the vents, the return openings, and all impediments in the basement, such as a water heater, hot water pipes, electrical boxes and fixtures. Flexduct must not come in contact with any heated element. Draw lines to show duct routes, then check them in the basement against the actual locations and distances.

Finish Basement After the Ductwork

• Install basement ductwork before any partition walls or basement ceilings are added. It's easiest with an open basement ceiling, but the ductwork can be framed in and covered with wallboard later if a finished ceiling is wanted. Generally, basements are built high enough to accommodate ductwork inside a finished ceiling.