plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delivery ...

, a Fixture Unit (FU) or Drain Fixture Unit (DFU) is "a unit of measure, based on the rate of discharge, time of operation and frequency of use of a fixture, that expresses the hydraulic load imposed by that fixture on the sanitary plumbing installation". A Fixture Unit is not a flow rate unit but a design factor. A fixture unit is equal to of water drained in a diameter pipe over one minute. Available at: https://mycomfortheroes.com/expert-tips/what-is-dfu-drainage-fixture-unit/ ccessed March 14, 2020/ref> One cubic foot of water is roughly . 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 In science and technology, an arbitrary unit (abbreviated arb. unit, '' see below'') or procedure defined unit (p.d.u.) is a relative unit of measurement to show the ratio of amount of substance, intensity, or other quantities, to a predetermined r ...

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 while 2000 FU represents only , about 1.5 times the flow rate. Fixture unit values can be determined using charts from the

International Plumbing Code The International Plumbing Code is a plumbing code and standard that sets minimum requirements for plumbing systems in their design and function, and which sets out rules for the acceptance of new plumbing-related technologies. It is published by th ...

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

Plumbing Units of flow {{Fluiddynamics-stub