How many measurements should be made when traversing a 10 inch by 20 inch duct?

When traversing a duct for airflow measurement, the total number of measurement points is often determined by the dimensions of the duct and specific methodologies used, such as the ASHRAE guidelines. For a rectangular duct, the common practice is to use a grid-based approach to calculate the number of data points needed for a representative sampling.

In a duct measuring 10 inches by 20 inches, it is standard to take measurements at the center and at specified intervals across both the width and the height. The total number of measurement points is typically determined by multiplying the number of intervals along the width by the number of intervals along the height.

A standard interval for traversing ducts is often derived from the geometry of the duct. For a rectangular duct, if one were to take measurements at every 1/4th of the width and height, the number of points collected could be expressed as follows: Taking measurements on the shorter side (10 inches), 2 points are taken (0 inches and 10 inches), while on the longer side (20 inches), 3 points are normally taken (0, 10, and 20 inches). Combining these points typically leads to a calculation that yields 3 x 4 = 12, 4 x