Calculate daily hot water demand and get a recommended storage cylinder size or continuous flow kW rating.
For 4 people at standard usage (70 L/person/day), you need 280 L/day. A 315 L storage cylinder is the appropriate next standard size up, providing full recovery overnight. This calculator recommends the correct standard tank size.
For a household of 4 with 2 simultaneous showers (12 L/min) and a 35°C temperature rise, you need approximately 35 kW. Most residential continuous flow units are 16–32 kW; commercial properties may require larger units.
Storage cylinders are simple and resilient but have standby heat loss. Continuous flow heaters are more energy efficient and endless supply, but need higher gas flow rates or electrical capacity. The right choice depends on your energy source, peak demand, and installation constraints.