Fixture unit
Encyclopedia
In plumbing
, a Fixture Unit (FU) is equal to one cubic foot
of water drained in an 1 1/4 pipe over one minute. A Fixture Unit is not a flow rate unit but a design factor. One cubic foot of water is roughly 7.48 gallon
s ( 6.25 Imperial Gallons) 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 gpm, but 2000 FU is not double that, but is only 1.5 times as much, or 330 gpm.
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 or
Plumbing
Plumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
, a Fixture Unit (FU) is equal to one cubic foot
Cubic foot
The cubic foot is an Imperial and US customary unit of volume, used in the United States and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.-Conversions:- Symbols :...
of water drained in an 1 1/4 pipe over one minute. A Fixture Unit is not a flow rate unit but a design factor. One cubic foot of water is roughly 7.48 gallon
Gallon
The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry...
s ( 6.25 Imperial Gallons) 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
Arbitrary unit
In science and technology, an arbitrary unit or procedure defined unit is a relative unit of measurement to show the ratio of amount of substance, intensity, or other quantities, to a predetermined reference measurement...
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 gpm, but 2000 FU is not double that, but is only 1.5 times as much, or 330 gpm.
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 or