What factors do fixture units (FUs) account for?

Fixture units (FUs) are a measure used in plumbing design to account for the demand on a plumbing system from various fixtures. The correct factor that fixture units consider is the probability of simultaneous use of fixtures. This is essential because not all fixtures in a plumbing system will be used at the same time, and the design must accommodate for the peak load while considering the likelihood of multiple fixtures being in use concurrently.

The concept of fixture units helps to quantify the total potential demand on a plumbing system by using a statistical approach to estimate how many fixtures are likely to be used at the same time. This probabilistic assessment is crucial for ensuring that the plumbing system can handle peak demands without unnecessary over-design or cost.

Factors like discharge flow rates, application with fixture size, and distance from discharge points, while important in plumbing design, do not directly pertain to the determination of fixture units. Discharge flow rates focus specifically on the capacity of drainage systems, application and fixture size relate to the specifics of individual fixtures' capacities, and distance from discharge points involves considerations of friction loss and pipe sizing rather than simultaneous usage probabilities.