Hot water wait calculator
Dead-leg volume model. We treat the pipe as full of cold water at startup and flush at steady GPM from the fixture. Mixing valves, parallel branches and recirc pumps are not modeled — use the result as a sales conversation starter for recirc or point-of-use heaters.
Example: lav ~1.5, kitchen ~2.2, tub fill higher.
Cold slug volume (approx)1.13 gal
Time to purge at stated GPM27 sec
Key takeaways
- Shows both gallons in the pipe and purge time.
- Three common nominal sizes preloaded.
- Explains dead-leg concept for circ pump upsells.
- No cloud upload of floor plans.
- Pairs with Jobber follow-up emails after the visit.
Who built this
ContractorHQ is edited by Bernard Guido — 25+ years in trade operations and software. These utilities follow the same quality bar as our reviews: fast pages, honest disclosure, and tools that stay useful without selling your data.
Frequently asked questions
PEX or CPVC?
This version uses approximate Type L copper IDs. For PEX, measure actual OD/ID from the spec sheet and use a custom equivalent length in a spreadsheet.
Recirculation pump?
If a pump keeps the line hot, the wait collapses — tell the homeowner that verbally; we do not model pump curves here.
Temperature mixing?
Not modeled. Output is hydraulics only for the cold slug volume story.
Why seconds not minutes?
Short dead legs clear fast at tub GPM; we show seconds for honesty, then you translate to customer language.