Ductwork is composed of two parts: supply and return. Supply ducts deliver air to each zone in a home. The amount of air reaching each zone is determined by the size of supply ductwork connected to your system.
Your contractor will help you determine the size of all the supply ductwork in your home. Ask your contractor to size the duct system according to ACCA Manual D calculation procedures.
The return ductwork attaches to the inlet of the new system and draws air out of the spaces to be heated or cooled. Attached to the return duct is the filter. The filter should be placed as near to the furnace or air handler as possible. Ductwork can be made either of fiberglass or metal, and must be properly sized in order to evenly distribute the proper amount of air to each room.