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Hot-Water Pipe Volume and Delivery Test

Calculate stored water and ideal purge time from actual pipe inside diameters, then record measured arrival time, volume and the stated temperature criterion.

Use this result well

Inputs that matter
Hot-water path segments, Additional stored volume (US gal), Actual hot-path flow (US GPM), Sources and assumptions, and 4 more
Output to expect
Pipe volume and ideal purge time, Measured hot-water delivery test
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Pipe volume and ideal purge time

Sum actual inside-diameter pipe segments and additional stored volume from the hot source to a fixture. Divide by the actual hot-path flow to estimate an ideal displacement time.

Pipe gallons = Σ π × inside diameter(in)² / 4 × length(ft) × 12 / 231; ideal purge seconds = total gallons × 60 / hot-path GPM.

Measured hot-water delivery test

Record elapsed time, collected water and outlet temperature against a stated delivery-temperature criterion. Keep the criterion and test conditions with the saved case.

Average collected flow = collected US gal × 60 / elapsed seconds; temperature criterion is met when the observed outlet temperature reaches the entered target.

Updated: September 2026

Example Scenarios

Try this example to see the calculation, then enter actual documented values and preserve the measurement conditions. A failed or unresolved comparison is part of the record.

→ 17.032726 seconds ideal purge

Try this example to see the calculation, then enter actual documented values and preserve the measurement conditions. A failed or unresolved comparison is part of the record.

→ Entered temperature criterion reached

FAQ

Sum actual inside-diameter pipe segments and additional stored volume from the hot source to a fixture. Divide by the actual hot-path flow to estimate an ideal displacement time. Record elapsed time, collected water and outlet temperature against a stated delivery-temperature criterion. Keep the criterion and test conditions with the saved case.

Use the exact equipment data, measurement point, operating conditions and units described in the selected mode. Record source documents, dates and unresolved conditions in Sources and assumptions. Built-in examples illustrate arithmetic; they are not manufacturer ratings or approved designs.

Use Save planning case for an explicit local history entry. Copy MD keeps current inputs and notes; Download CSV exports the result breakdown. Export portable copies before clearing storage and save a separate case after changing equipment, conditions or measurements.

About Hot-Water Pipe Volume and Delivery Test

Sum actual inside-diameter pipe segments and additional stored volume from the hot source to a fixture. Divide by the actual hot-path flow to estimate an ideal displacement time. Record elapsed time, collected water and outlet temperature against a stated delivery-temperature criterion. Keep the criterion and test conditions with the saved case.