Convention Applied by the app plumb.water.velocity
Design velocity for water pipe
The velocity the app sizes a water run to, 8 feet per second cold and 5 feet per second hot. Design practice under the IPC, which prints no velocity limit; the UPC caps copper tube at the same figures.
| When | The app uses |
|---|---|
| Cold water | 8 fps |
| Hot water | 5 fps |
- Source
- ASPE · Plumbing Engineering Design Handbook, Vol. 2, Ch. 5 (cold water) and Ch. 6 (hot water), velocity limits; Copper Development Association, Copper Tube Handbook, "velocity" (5 fps hot, 8 fps cold) · read the public text
- Editions checked
- —
- Used by
- Water Sizing
- Amendments
No state or local amendment to this rule is on file. Not on file means the model code as written — check your jurisdiction.
A working figure the trade uses and the app defaults to. Shops override these most.
The IPC prints no velocity limit for water pipe. Its Appendix E sizes by the pressure available and the developed length of the critical run, at a velocity the designer selects from the pipe makers' recommendations. The Uniform Plumbing Code does print one: a copper or copper-alloy tube system runs no faster than 8 feet per second cold and 5 hot (610.12 in the 2021 edition). So in a UPC state the two caps are code; under the IPC they are the trade's design practice. Either way the reason is the same: fast water erodes fittings, hammers valves and is loud in a wall. The same 8 and 5 are what most design guidance agrees on, and what an estimator pencils in on a walk-through. Hotter water wants less: above 140 °F the Copper Tube Handbook keeps hot water to 2 to 3 feet per second.
What the app does with it
The size suggestion at the S moment (rung 4 of the water-sizing ladder) is the smallest nominal size whose velocity, at the design flow for the fixture units still to serve, stays under the cap for the run's side. The two caps are knobs on the Water Sizing schedule (rung 5) and stick with the project; the schedule foot stamps the result "sized at 5 / 8 fps; the pressure check is Bid Check's" so nobody mistakes a rule of thumb for a design. The app keeps one hot cap per project and does not know the water's temperature: on a job whose hot loop runs above 140 °F (a recirculated or a 160 °F kitchen loop), lower the hot cap on the schedule.
What it does not do
It does not check the pressure at the farthest fixture. That is Appendix E's full calculation and stays a manual Bid Check row, Pressure available checked (Appendix E), until the critical-path math exists.
Verify against your edition
The UPC figure was read in a state's adoption of the UPC 2021, not in IAPMO's own book; a UPC jurisdiction reads its adopted section. A jurisdiction or an engineer may set lower caps, and the schedule's knobs take them. Settled 2026-09-27 by Claude on the owner's delegation, from the dossier's research and the model code text; not checked against a printed book or a local amendment.
Cited by section, not reprinted: the code text belongs to its publisher. Company practice is not a rule here — it lives with your pricing.