WSFU are used to determine water supply to fixtures and their service systems
The Water Supply Fixture Units (WSFU) are defined by the Uniform Plumbing Code (UPC), and can be used to determine the water supply to fixtures and their service systems.
|Individual Fixtures||Minimum Fixture Branch Pipe Size||Water Supply Fixture Units |
|(inch)||Private Installations||Public Installations|
|Bathtub with 3/4" fill valve||3/4||10||10|
|Clinic fauce sink||1/2||3|
|Kitchen sink, domestic||1/2||1.5||1.5|
|Service or mop basin||1/2||1.5||3|
|Urinal with flush tank||1/2||2||2|
|Water closet with gravity tank||1/2||2.5||2.5|
|Water closet with flushometer tank||1/2||2.5||2.5|
- 1 WSFU = 1 GPM = 3.79 liter/min
Note that this conversion is true only for one or a few fixtures. Since the fixtures in a system are never used all at the same time, the total units achieved by adding the numbers for all fixtures must be compensated for intermittent use.
For supply pipe lines this is taken care of in the sizing tables.