The method
Before using the result
- Ideal mixing of the same liquid, constant heat capacity and density, with no heat loss or phase change. This does not select scald protection.
Worked examples
These original training examples illustrate the method for Journeyman Plumber (JP). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Find hot and cold proportions for an ideal plumbing mixing exercise. Check that the target temperature lies between the two supplies before calculating quantities.
- Hot temperature
- 60 °C
- Cold temperature
- 10 °C
- Target temperature
- 40 °C
- Quantity basis
- Volume
- Total volume
- 100 L
- Hot fraction = (40 − 10) / (60 − 10) = 0.6.
- Hot quantity = 0.1 × 0.6; cold quantity = 0.1 × 0.4.
- Hot proportion: 60 %
- Cold proportion: 40 %
- Hot quantity: 0.06 m³
- Cold quantity: 0.04 m³
2. Comparison example
Compare a different supplied condition using the same method. For Plumber Conquer, the important check is that the input meaning, units and method assumptions still match the problem.
- Hot temperature
- 60 °C
- Cold temperature
- 10 °C
- Target temperature
- 35 °C
- Quantity basis
- Volume
- Total volume
- 100 L
- Hot fraction = (35 − 10) / (60 − 10) = 0.5.
- Hot quantity = 0.1 × 0.5; cold quantity = 0.1 × 0.5.
- Hot proportion: 50 %
- Cold proportion: 50 %
- Hot quantity: 0.05 m³
- Cold quantity: 0.05 m³
Check your understanding
1. Which relationship is used?
Hot fraction = (Ttarget − Tcold)/(Thot − Tcold).
2. Which assumption should you check first?
Ideal mixing of the same liquid, constant heat capacity and density, with no heat loss or phase change. This does not select scald protection.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
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