A Combined Tank (Two-in-One Tank) refers to a combined water storage solution that integrates both a domestic hot water (DHW) tank and a buffer tank within a single unit. Instead of installing separate tanks for hot water storage and heating system buffering, this dual-compartment design consolidates both functions, saving space and simplifying installation. One internal tank is dedicated to storing sanitary hot water for daily use, while the other acts as a buffer for heating systems such as heat pumps, solar thermal systems, or electric heaters. Built-in heat exchanger coils allow efficient transfer of thermal energy between the heating source and the stored water. Two-in-one tanks are typically constructed with corrosion-resistant stainless steel and high-efficiency insulation, providing durable performance with reduced heat loss. By combining storage and buffer capabilities, these tanks improve system efficiency, reduce piping complexity, and are well suited for residential and commercial hot water and heating applications.