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Standards Development
This document is applicable to gas-fired appliances producing domestic hot water. It applies to sorption heat pumps connected to or including a domestic hot water storage tank. It applies to a package marketed as single unit or fully specified that have:
- a heat input not exceeding 400 kW;
- a hot water storage tank capacity (if any) not exceeding 2 000 l.
In the case of gas-fired sorption heat pumps, with or without storage tank, domestic hot water production is integrated or coupled, the whole being marketed as a single unit.
EN 13203-1:2025 sets out in qualitative and quantitative terms the performance in delivery of domestic hot water for a selected variety of uses. It also gives a system for presenting the information to the user. The present document sets out a method for assessing the energy performance of the appliances. It specifies a number of daily load profiles for each domestic hot water use, kitchen, shower, bath and a combination of these, together with corresponding test procedures, enabling the energy performances of different gas-fired appliances to be compared and matched to the needs of the user. Where other technologies are combined with a gas-fired sorption heat to produce domestic hot water, specific parts of EN 13203 apply.
Horizontal ground heat sources are not covered by the scope of the present document.
EN 13203-6 is part of the EN 13203 series, which defines methods for assessing the energy performance of domestic hot water systems. Part 6 specifically addresses systems of multiple water heaters connected in series or parallel, including cascaded or modular arrangements.
The standard provides a harmonised test and calculation method to determine the energy efficiency, heat losses and performance indicators of multi-water-heater installations under representative load conditions. It ensures that such systems can be evaluated consistently, transparently and comparably across the European market, regardless of manufacturer or system configuration. With increasing deployment of modular, cascaded and hybrid DHW systems—often driven by higher efficiency requirements, renewable integration and load flexibility—existing single-appliance test methods are no longer sufficient. EN 13203-6 fills this gap by:
• capturing hydraulic and thermal interactions between multiple heaters,
• accounting for control strategies and load-sharing effects, and
• enabling fair comparison between centralised, decentralised and modular DHW concepts.
The standard supports EU energy efficiency and ecodesign frameworks, helps regulators and planners assess real system performance, and gives manufacturers a clear, technically robust basis for product declaration and system optimisation.
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