Drainage Fixtures - Unit Loads and Sanitary Piping
Maximum Drainage Fixture Unit - DFU - loads for sanitary piping
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The relationship between volume flow and fixture units is not constant, but varies with the number of fixture units. A Fixture Unit is not a flow rate unit but a design factor based on the rate of discharge, time of operation and frequency of use of a fixture. A fixture unit is equal to one cubic foot of water drained in an 1 1/4 pipe over one minute (≈ 7.48 US gpm, ≈ 0.47 l/s).
Maximum Drainage Fixture Units (DFU) in Stacks and Horizontal Fixture Branches
| Maximum Drainage Fixture Units (DFU) | |||||
|---|---|---|---|---|---|
| Pipe Size | Horizontal fixture branch | Stacks less than three stories in height | Stacks more than three stories high | ||
| NPS (inches) | DN (mm) | ||||
| Total for stack | Total for one story | ||||
| 1 1/20) | 40 | 3 | 4 | 8 | 2 |
| 20) | 50 | 6 | 10 | 24 | 6 |
| 2 1/20) | 65 | 12 | 20 | 42 | 9 |
| 3 | 80 | 201) | 481) | 722) | 201) |
| 4 | 100 | 160 | 240 | 500 | 90 |
| 5 | 125 | 360 | 540 | 1100 | 200 |
| 6 | 150 | 620 | 960 | 1900 | 350 |
0) No water closet permitted
1) Maximum two water closets
2) Maximum six water closets
Maximum Drainage Fixture Units (DFU) in Building Drains and Building Drain Branches from Stacks
| Maximum Drainage Fixture Units (DFU) | |||
|---|---|---|---|
| Pipe Size | Slope (in/ft (cm/m)) | ||
| NPS (inches) | DN (mm) | ||
| 1/4 (2.1) | 1/2 (4.2) | ||
| 20) | 50 | 21 | 26 |
| 2 1/20) | 65 | 24 | 31 |
| 3 | 80 | 421) | 501) |
| 4 | 100 | 216 | 250 |
| 5 | 125 | 480 | 575 |
| 6 | 150 | 840 | 1000 |
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