Main Duct View
Duct View continued
Supply / return estimated area - These are estimates of the total surface area of the ductwork, in a manner similar to entering the total area of a wall or window. Start with an estimate of the length of each duct runs and their corresponding size. Using the size calculate the perimeter length of the duct (how far around) in inches. Divide the perimeter length by twelve (12) to yield decimal feet. Multiple the perimeter length (in decimal feet) by the length of the run to get the surface area (in square feet) of that particular run. Sum up the surface area of all the supply runs for supply estimated area, and all the return runs for return estimated area.