Cold plunge guide

Cold Plunge Commissioning: Leak Test, Flow Test & First Cooldown

A system is not finished when the fittings are tight. It is finished when the installed loop has been measured and behaves within a credible range.

Updated Aug 21, 202610 min readManufacturer + engineering sources
The first startup is a validation test

Leak-test, prime, measure flow, cross-check temperature and log the first cooldown. The measurements become your future troubleshooting baseline.

1. Before filling

  • Connections match and components are supported.
  • Chiller flow and pressure limits are documented.
  • Condenser airflow is clear.
  • Electrical/GFCI/RCD requirements are satisfied.
  • Valves are in the correct operating position.

2. Circulation-only leak test

Fill and run the pump with refrigeration off. Inspect bulkheads, threaded joints, filter housings, unions and chiller ports. Dry suspected areas and check again.

3. Prime and purge

Follow pump instructions and do not run non-self-priming pumps dry. Purge air from housings and lines. Air can reduce flow and cause noise.

Commission the same loop you designed. Compare measured flow with the model and the chiller minimum after the filter is installed.

Check modeled flow

4. Measure flow

Safely divert the return into a known container if the plumbing allows it. Time, calculate GPH, repeat and average. Compare with the chiller minimum and calculator range.

5. Cross-check temperature

Use an independent thermometer in well-mixed water to compare the chiller sensor during the first run.

6. Log the first cooldown

Record start temperature, ambient, exposure and water temperature every 30–60 minutes. Compare only after the run; do not tune the prediction while watching the result.

7. Save a baseline

Keep clean-filter flow, normal cooldown and typical compressor cycling. Later, a change in any of these becomes a diagnostic clue.

8. Turn the first run into measured numbers

For a timed-container flow check, use GPH = container gallons × 3,600 ÷ fill seconds. Repeat the measurement several times and use the average. For example, if 5 gallons fills in 30 seconds, the measured return is 600 GPH. Use a method that can be performed safely without exposing energized equipment to water.

For cooldown, record the actual water temperature change over a known period rather than judging by touch. A stable mixed-water reading lets you compare one commissioning run with a later diagnostic run under similar ambient conditions.

Acceptance itemPass conditionSave as baseline
LeaksNo active seepage at operating circulationPhotos of joints and valve positions
FlowInside the chiller requirement with marginMeasured GPH and filter state
TemperatureIndependent thermometer is reasonably consistent with control readingBoth readings
CooldownTrend is consistent with the modeled range and installation conditionsStart, target, ambient and elapsed time
Air sideRequired chiller clearances remain unobstructedInstallation photo

9. Re-test after the system has been used

A first-day pass proves only the clean system. Re-check flow after the filter has accumulated normal debris and compare it with the commissioning baseline. If the drop is large, shorten the service interval or reduce hydraulic restriction before it becomes a chiller-flow problem.

Commissioning record

Keep a simple log: date, starting water temperature, target, ambient, sun/shade, clean-filter state, measured or modeled flow, and time to target. This record is more useful than a generic online benchmark because it describes your exact equipment and installation.

Related system resources

Run your exact setup

Use your real tub, temperature, ambient, exposure, pump, filter and plumbing. ChillSizer checks thermal capacity and real operating flow together.

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