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Water Heater Capacity Calculator — Free Online Calculator

Estimates the required storage water heater capacity for household needs.

What is it?

The water heater (boiler) capacity calculator determines the minimum tank size or flow rate needed for a household based on the number of users, shower duration, and flow rate.

Formula

Daily hot water volume (L) = People × Showers per day × Duration (min) × Flow rate (L/min) Tank capacity needed ≥ Peak demand volume Heating time (hr) = Tank volume (L) × ΔT (°C) × 0.00116 / Heater power (kW)

Example

3 people, 1 shower each per day, 8 minutes, showerhead flow 8 L/min. Daily volume = 3 × 1 × 8 × 8 = 192 L. A 200 L tank (or 80 L tank with 2.5 kW fast reheat) covers this comfortably.

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