Calculation sequence
Step-by-step method
- Calculate the hot-water fraction from the three temperatures.
- Divide stored hot volume by the hot fraction.
- Subtract stored hot volume for required cold-water volume.
PlumbingIntermediateDomestic Hot Water
Mixed-Water Storage Yield Calculator
Estimate ideal deliverable mixed-water volume from stored hot water and selected hot, cold, and delivery temperatures.
Why it matters: Stored volume and deliverable mixed volume are different when a mixing valve blends cold water.
Calculated result
Engineering evaluation
Deliverable mixed-water volume (Vᵐ)133.333 gal
- Required cold-water volume (Vᶜ)
- 33.333 gal
- Hot-water fraction (xʰ)
- 75 %
Engineering interpretation
100 gal of entered usable storage ideally yields 133.3333 gal mixed water at 75% hot fraction.
Important limitations
- Ideal mixing only. Stratification, dead volume, draw pattern, recovery, valve authority, piping heat loss, temperature-control, scald, and Legionella-risk requirements require explicit project and professional review.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
xʰ=(Tᵐ−Tᶜ)/(Tʰ−Tᶜ)
Vᵐ=Vʰ/xʰ
Vᶜ=Vᵐ−Vʰ
Current substitution
xʰ=(120−60)/(140−60)=0.75; Vᵐ=100/0.75=133.3333; Vᶜ=33.33333.
Equation legend
Inputs and calculated quantities
- Vʰ
- Available stored hot-water volume — gal or L
- Tʰ
- Stored hot-water temperature — °F or °C
- Tᶜ
- Cold-water temperature — °F or °C
- Tᵐ
- Mixed delivery temperature — °F or °C
- Vᵐ
- Deliverable mixed-water volume — gal
- Vᶜ
- Required cold-water volume — gal
- xʰ
- Hot-water fraction — %
Applications
How this calculation is used
Building design
Screen the effect of storage temperature on mixed-water yield.
Construction
Check scheduled tank and mixing-temperature assumptions.
Commissioning
Document the ideal mixing relationship before field capacity verification.
Quality controls
Assumptions and limitations
Assumptions
- Entered values describe one documented system and use a consistent unit, energy, pressure, elevation, and measurement basis.
- Measurements are representative and synchronized where the calculation combines field readings.
Limitations
- Ideal adiabatic mixing omits stratification, dead volume, recovery, draw pattern, distribution heat loss, and valve capacity.
- Temperature-control, scald-protection, Legionella-risk management, and usable-storage criteria require approved policies and listed devices.
Field use
Verification procedure
- Confirm the calculation boundary, source documents, formula symbols, and units.
- Record representative field values or approved project inputs and their sources.
- Review the result against the applicable code, criteria, manufacturer data, and measurement uncertainty.
Common engineering mistakes
- Combining values from different system boundaries, operating periods, temperature bases, or unit conventions.
- Treating a calculated screening value as a hidden pass/fail threshold or final design decision.
Technical basis
References and source standards
- ASSE Product Performance StandardsASSE 1017 and other applicable standards provide product context for hot-water mixing and temperature-control devices.
- International Plumbing Code, 2024The legally adopted edition and local amendments govern water, sanitary, storm, sump, and pumping requirements; protected code tables are not reproduced.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement