The total fabrication and installation costs of the sheet metal duct work shown in the Design Criteria page are plotted above, and are based on the following sizes:

Round spiral duct 32 inch diameter to 14 inch diameter.
Flat oval spiral duct 60 x 16 inch 10 14 inch diameter.
Rectangular duct 60 x 16 inch to 12 x 14 inch

All three duct systems were sized to have approximately the same static pressure drop.

The estimated costs were obtained recently from sheet metal contractors in nine different cities throughout the U.S.A. and Canada.