Appliances & Utilities calculator
What Hot Water Cylinder Capacity Do I Need?
Find minimum stored hot-water volume from household members, daily/peak stored hot water per person, and largest simultaneous bath/shower draw.
Enter your measurements
What Hot Water Cylinder Capacity Do I Need? Start with household members, daily/peak stored hot water per person, and largest simultaneous bath/shower draw. This minimum-capacity calculation turns those measurements into minimum stored hot-water volume, so you can compare real products or available space before making a decision.
- Household members — Required
- Daily/peak stored hot water per person — Required
- Largest simultaneous bath/shower draw — Optional
- Fraction recovered during peak period — Required
Minimum stored hot-water volume
Enter the measurements above to calculate minimum stored hot-water volume.
How the calculation works
Behind the calculator, the rule is basePeakDemand=max(people×hotWaterPerPerson,simultaneousBathVolume); storageNeed=max(0,basePeakDemand×(1-recoveryFraction)). That rule maps directly to the displayed minimum stored hot-water volume.
Worked example
Example: Household members = 4; Daily/peak stored hot water per person = 45 L; Largest simultaneous bath/shower draw = 120 L; Fraction recovered during peak period = 20%. Result: Storage Need = 144 L; Base Peak Demand = 0.18.
Before you decide
Measure the actual item, opening or body dimension involved. This page calculates the stated geometry or quantity only; product-specific construction or installation details can still affect the final choice. For what hot water cylinder capacity do i need, the limiting result on this page is minimum stored hot-water volume.
Direct measurement/geometry calculation. No external reference is required for the arithmetic itself; the result is derived only from the user-entered measurements and the formula stored in calculationLogicJson.
Frequently asked questions
How does the Hot Water Cylinder Capacity | Capacity Guide calculator work?
It uses basePeakDemand=max(people×hotWaterPerPerson,simultaneousBathVolume); storageNeed=max(0,basePeakDemand×(1-recoveryFraction)). The result is minimum stored hot-water volume.
Which measurements or specifications do I need?
Use these inputs: Household members, Daily/peak stored hot water per person, Largest simultaneous bath/shower draw, Fraction recovered during peak period. Measure or copy the values from the exact product/specification rather than guessing.
Is the result a guarantee that the product will fit or be suitable?
No. The calculator answers the stated minimum stored hot-water volume question. Manufacturer instructions, safety rules, certification, installation tolerances or brand-specific size charts can impose additional requirements.