Working With a Duct Board

Plan the duct board installation. Use a floor plan of the house to diagram all locations for duct board. Indicate sizes such as 8-inch by10-inch, 14-inch by 16-inch or other dimensions. Start where the heating/cooling unit's supply and return openings enter the house. Indicate all vents and return openings and show any electrical, hot water or other obstacles.

Combine duct board with flex duct for maximum efficiency. Ductwork must be balanced to operate efficiently; that requires a return system to take "used" air from the house back into the unit, with the same capacity as the supply --- the airflow coming in from the unit. Duct board is formed into squares and rectangles; flexduct is round. Air flows more efficiently through round openings.

Use duct board for the primary openings and for any locations where flex duct cannot be fitted. Some systems must route duct work through ceilings or in wall cavities where flex duct will not fit or may be ineffective. Use duct board to fit these special requirements. A 12-inch flex duct won't fit between 2-inch by 4-inch wall studs, so form duct board to fit that cavity. Use this technique when duct work must be run up walls between floors or between ceiling joists. Buy elbows for sharp turns and sheet metal connectors to join duct board or flex duct sections.

Form duct board by cutting to size and using special tools which cut tongues and grooves that fit together when the duct board is folded into shape. The final seam is formed by stripping the fiberglass down to the facing to form a stapling strip, which is folded over the next panel and secured with special staples. Seal joints with a special heat-resistant tape.