Difference between a hot water boiler and a heating boiler
Both in everyday life and in technical contexts, the terms hot water and heating water are often used interchangeably. There are various definitions, which sometimes make it difficult to draw a clear distinction between them.
In normal (non-technical) usage, heated potable or service water is referred to as hot water from 60 °C upwards due to the risk of scalding.
In boiler technology, however, this limit is set at a maximum permissible temperature of 110 °C. If the maximum permissible temperature, i.e. the setting of the safety temperature limiter, is above 110 °C, these are referred to as hot water boiler systems. If the safety temperature limiter is set to a maximum of 110 °C, the system is referred to as a boiler system.
The maximum permissible temperature in the system represents an important legal limit which has a significant influence on the design, manufacture, CE marking, installation and operation of a hot water and boiler system in all the areas mentioned.
This limit is defined in the European Pressure Equipment Directive 2014/68/EU with a maximum permissible overpressure of more than 0.5 bar (relevant for steam) or a maximum permissible temperature of 110 °C (relevant for water).
For water, the boiling point at an overpressure of 0.5 bar is 110 °C.
All hot water boiler systems whose safety temperature limiters are set above 110 °C are therefore covered by the Pressure Equipment Directive and are handled in the same way as steam boiler systems with regard to legal requirements. This classification applies not only to the boiler itself, but to all components used in the hot water boiler system, such as fittings, pipes and heat exchangers at the consumers.
Heat generators that are in the range of ≤ 110 °C safety temperature fall under the Gas Appliances Regulation 2016/426/EU, or are certified according to the Gas Appliances Regulation. In these systems, maximum flow temperatures of up to 103 °C can be reached during operation and they are somewhat more favourable in terms of their costs, not only for installation but also for supervision and monitoring.
In the Bosch technical guide, hot water and heating systems are referred to equally when either of the two terms is used. Any differences will be expressly pointed out.