How do you calculate the basic area of a duct?

To calculate the basic area of a duct, the most appropriate formula is length multiplied by width. This is grounded in the principles of geometry where the area of a rectangle (which is the typical shape of a duct) is determined by the product of its two dimensions: the length and the width.

When using this formula, you gather the measurements of the duct's internal dimensions to ensure that you are working with the actual cross-sectional area that will allow for accurate airflow calculations, important in HVAC system design. By using length and width in this manner, you can determine the area in square units, which is crucial for sizing ducts appropriately for the demands of the heating, ventilation, and air conditioning system.

The other options don't mathematically yield the area and are not applicable for this context. For example, adding dimensions or subtracting them does not provide information about the area of a two-dimensional shape; likewise, dividing length by width doesn’t give an area result. Hence, multiplying length by width is the only effective method to find the area of a duct.