Fixture units are based on which of the following factors?

Fixture units are a key concept in plumbing design, serving as a standardized way to estimate the demand on a plumbing system from various fixtures. The correct answer relates to how fixture units are determined by assessing the weight of fixtures in relation to the water supply load. This concept is critical because it allows designers to quantify the potential water flow demands based on different types and combinations of plumbing fixtures installed in a building.

When plumbing designers calculate fixture units, they take into account not only the type of fixtures installed but also how those fixtures will interact with one another under various conditions. This includes understanding the flow characteristics and the demands they will place on the water supply system. By assigning specific fixture units to different fixtures based on their expected usage, designers can effectively size pipes, water supply lines, and the overall plumbing system to ensure adequate water delivery and pressure, ultimately optimizing performance and efficiency.

In contrast, factors such as time of usage, type of pipe used, and the location of fixtures do not directly influence the assignment of fixture units. While they are important in overall plumbing design and system planning, they do not alter the fundamental calculation of fixture units, which focuses on weight and associated flow demands relative to the water supply load.