Drainage Fixture Unit Values - DFU
DFU are used to determine the drainage from fixtures and required capacity of sewer service systems
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DFU (Drainage Fixture Unit Values) is defined by the the Uniform Plumbing Code (UPC) and can be used to determine required drainage capacities from fixtures and their service systems.
| Individual Appliance, Appurtenance or Fixture | Minimum Size | Drainage Fixture Unit Values (DFU) | |
|---|---|---|---|
| (inch) | Private Installations | Public Installations | |
| Bar sink | 1 1/2 | 1 | 1 |
| Bathroom (water closet, lavatory, bidet and tub or shower) | 3 | 6 | - |
| Bathtub | 1 1/2 | 2 | 2 |
| Bidet | 1 1/4 | 1 | |
| Bidet | 1 1/2 | 2 | |
| Clothes Washer | 2 | 3 | 3 |
| Dishwasher, domestic | 1 1/2 | 2 | 2 |
| Drinking fountain | 1 1/4 | 0.5 | 0.5 |
| Floor drain | 2 | 2 | 2 |
| Shower | 2 | 2 | 2 |
| Laundry tub | 1 1/2 | 2 | 2 |
| Lavatory | 1 1/4 | 1 | 1 |
| Bar sink | 1 1/2 | 1 | |
| Kitchen sink, domestic | 1 1/2 | 2 | 2 |
| Laundry sink | 1 1/2 | 2 | 2 |
| Service or mop basin | 2 | 3 | |
| Urinal | 2 | 2 | 2 |
| Water closet with gravity tank | 3 | 3 | 4 |
| Water closet with flushometer tank | 3 | 3 | 4 |
- 1 WFSU = 1 GPM = 3.79 liter/min
Note that this conversion is only true for one or a few fixtures. Since the fixtures in a system are never used all at the same time, the total units (capacity) achieved by adding the numbers for all fixtures must be compensated for intermittent use if we want a realistic estimate of the total drainage load.
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