How do I convert fixture units to GPM?

Q: How many fixture units is a toilet?

Under the IPC, a residential flush-tank water closet is 3 DFU for drainage; under the UPC it is typically counted as 3–4 DFU. A flushometer (commercial) water closet is higher, often 6 DFU. On the water-supply side a tank-type toilet is about 2.2 WSFU. Always use the table that matches your adopted code and whether the use is private or public.

Q: What is the difference between DFU and WSFU?

Drainage fixture units (DFU) measure the load a fixture places on drain and vent piping; water supply fixture units (WSFU) measure the demand it places on the supply system. They are not interchangeable — a fixture has separate DFU and WSFU values, and you size drains from DFU totals and supply pipe from WSFU totals.

Question

How do I convert fixture units to GPM?

Accepted Answer

Use Hunter’s curve (the IPC water-supply demand chart): fixture-unit totals are converted to probable simultaneous demand in GPM, because not every fixture runs at once. Roughly, 10 WSFU is about 8 GPM and 100 WSFU is about 44 GPM, but the curve is nonlinear — read it from the code table rather than scaling linearly.

How do I convert fixture units to GPM?

Answers