Plan tank capacity using demand, temperatures, recovery, and reserve rules. Get practical sizing results for projects with confidence today.
| Project Type | Users | L/day per User | Peak % | Storage Temp °C | Delivery Temp °C |
|---|---|---|---|---|---|
| Small office | 20 | 45 | 35 | 60 | 50 |
| Clinic block | 35 | 55 | 40 | 65 | 50 |
| Worker housing | 60 | 50 | 45 | 60 | 48 |
1. Daily diversified demand
Daily Demand = Occupants × Daily Use per Person × Diversity Factor
2. Peak mixed demand
Peak Mixed Demand = Daily Demand × Peak Hour Percent
3. Hot fraction from the tank
Hot Fraction = (Delivery Temperature − Cold Temperature) ÷ (Storage Temperature − Cold Temperature)
4. Equivalent stored hot water
Equivalent Stored Hot = Peak Mixed Demand × Hot Fraction
5. Base storage
Base Storage = Equivalent Stored Hot ÷ Usable Tank Fraction
6. Final storage
Final Storage = Base Storage × (1 + Safety Factor) × (1 + Standby Allowance)
7. Recovery heater size
Heater kW = Heating Energy ÷ Recovery Time
Enter the expected number of users first. Add daily hot water use for each person. Set the percentage expected during the design peak. Enter cold, delivery, and storage temperatures. Then add usable tank volume, diversity, safety, standby allowance, and recovery time. Press the calculate button. The result block appears above the form. Review the suggested nominal tank size, recovery rate, energy, and heater capacity. Export the result as CSV or PDF when needed.
Hot water storage affects comfort and system reliability. A small tank causes shortages during peak demand. An oversized tank raises standby losses and equipment cost. Good sizing balances these issues. It also supports better planning during design and tender stages.
Begin with the actual user count. Then estimate daily hot water use per person. Different projects have different patterns. Worker housing, offices, clinics, and small commercial spaces rarely behave the same. A clear demand estimate prevents weak sizing assumptions later.
Most systems fail during peak draw periods. That is why the calculator includes peak hour share and draw duration. These inputs help you focus on the most demanding period. Storage should meet that period without large temperature drop at fixtures.
Stored water is usually hotter than delivered water. Mixing with cold water increases useful output. The calculator converts mixed demand into equivalent stored hot water. This gives a more practical tank requirement. It also shows why storage temperature strongly affects final capacity.
Not every litre inside a tank is fully usable. Dead zones, controls, and stratification reduce available storage. Safety and standby allowances improve reliability. These factors are useful for construction planning where occupancy changes or piping losses may be uncertain.
Tank sizing should not be separated from heater recovery. Faster recovery can reduce required storage. Slower recovery needs more stored water. The calculator estimates recovery volume per hour and heater power. This helps align the tank with the heat source and operating schedule.
This tool gives a practical preliminary estimate. Final selection should still consider local codes, Legionella control, insulation, heater type, and manufacturer data. Use the result to compare options, review assumptions, and prepare better construction decisions before final equipment selection.
It estimates practical hot water storage tank volume for a project. It also shows recovery rate, energy need, and suggested heater capacity.
Stored water is kept hotter so it can mix with cold water. That increases usable output and supports a smaller tank for the same delivered demand.
It is the percentage of the physical tank that can be used effectively. Control margins, stratification, and operating limits reduce full usable volume.
Safety factor covers uncertain usage, future growth, and short demand spikes. It helps avoid undersized storage in real operating conditions.
Diversity factor reduces total daily demand when all users are unlikely to draw at full expected usage. It reflects more realistic building behavior.
Yes. It can support early sizing for apartments, worker housing, offices, clinics, and similar projects when you have reasonable demand assumptions.
Usually yes. Faster recovery replaces used hot water sooner. That can lower stored volume, but heater capacity and operating cost must still be checked.
No. Use it as a preliminary design aid. Final procurement should match code rules, manufacturer data, heat source limits, and project-specific operating needs.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.