Fixture unit

Source: Wikipedia, the free encyclopedia.

In

imp gal
). A Fixture Unit is used in plumbing design for both water supply and waste water.

Different fixtures have different flow requirements. In order to determine the required size of pipe, an arbitrary unit is used for pipe sizing which takes into account the likelihood that all the fixtures will not be used at the same time. This is called "fixture unit" (FU). The relationship between gallons per minute (gpm) and fixture unit is not constant, but varies with the number of fixture units. For example, 1000 FU is equivalent to 220 US gallons per minute (0.014 m3/s) while 2000 FU represents only 330 US gallons per minute (0.021 m3/s), about 1.5 times the flow rate.

Fixture unit values can be determined using charts from the International Plumbing Code or similar codes in local jurisdictions.

There are situations where a design provides for more FUs being discharged than being supplied. This occurs in situations where liquids may infiltrate or are added to a draining system, such as might happen in a large sports venue. Examples of how this could occur include rain water infiltration.

References