Interpretation #8612
Published January 25, 2022
Original Request
- Code Version
- 2021
- Code
- PLUMBING
- Code Description
- Chapter
- Section
- 604.3
- Topic
- peak demand
Question
is it the intent of section 604.3 water distribution system design criteria , that under conditions of peak demand means one fixture from table 604.3 operating independently equates to the defining of peak demand
Answer Published 01/25/2022 at 9:25 AM
No. The purpose of Table 604.3 is to provide design criteria for the sizing of water distribution systems.
Commentary
Knowledge of a fixture’s flow rate is necessary to determine friction loss. The Table is not intended to serve as a field test for peak demand.
The code does not define peak water demand. It is unrealistic to assume all fixtures to be operating at the same time. According to Section 604.1, the design of the water distribution system shall conform to “accepted engineering practice.” One commonly used method can be found in Appendix E, which lists load factors for various fixtures, expressed in water supply fixture units (wsfu). The total wsfu’s are then converted to flow rates in gallons per minute, and applied to a chart to determine friction loss.
According to the IPC Commentary, the wsfu method may not provide suitable results for projects with very high or very low water demands. IAPMO has developed a downloadable Water Demand Calculator that accurately predicts peak water demand in single-family and apartment buildings.