DIN EN 12828, Heating systems in buildings

General Information

The DIN EN 12828 very generally describes the design criteria of hot-water heating systems. In particular, it addresses the areas related to heat generation plants, heat distribution systems and heat emission systems.

Since the DIN EN 12828 replaces (among others) the DIN 4751 T 1-3, the safety-related equipping of heat generators is also described here. The standard also includes an informative attachment for calculating pressurization systems because the DIN 4807 T2 is also partially replaced by the DIN EN 12828.

The competent reader will quickly notice that the normally clear and detailed speech is missing from the DIN 4751. This is most likely the result of the attempts at European harmonization and is also not otherwise possible as described in the standard by the Committee for Standardization Whether this results in a simplification in the application, however, remains to be seen.

All market partners, from the manufacturer to the planner and technician will have to get used to the standard, which is in many places free and loosely formulated. Reflex wants to make information available at this point which will provide the usual, clear overview and help to simplify working with the new rules.

Area of application

Only the "hot-water area" is referenced as area of applicability. The standard understands to mean systems whose heat generators work with a maximum operating temperature of 105 C. Meant here is not the maximum set temperature on the safety temperature limiter of the generator but rather the maximum selectable temperature on the regulator for the operation.

The maximum possible temperature setting for the safety temperature limiter is not numerically quantified in the DIN EN 12828. To the preliminary statement it is mentioned that, determined by the ancillary conditions of the Ordinance on Industrial Safety and Health (BetrSichV), and additional standards, such as the DIN EN 12952 and 12953 (equipping of boilers with operating temperatures above 100 respectively 110 C), this temperature for hot water systems must level off at a maximum temperature of 110°C in accordance with DIN EN 12828. Provided that securing temperatures >110°C is necessary during planning and construction of heat generation systems, we currently recommend consulting with the TÜV beforehand. The desired and required equipment for the determination of the inspection deadlines (BetrSichV) can be coordinated.

Start of the validity

The DIN EN 12828:2003 has been in force since July 4, 2002 and has the status of a German standard. The replaced standards were additionally valid, however, only until March 31, 2004.

Safety-related equipment (details)

  Summary of the DIN EN 12828

  • Overview "Safety-related equipment according to DIN EN 12828", direct heating
  • Comparison table "Safety technology DIN 4751 T2/ DIN EN 12828", direct heating
  • Comparison table "Safety technology DIN 4751 T2/ DIN EN 12828", direct heating

Comments of the BHKS, ZVSHK and DIN

A comment on the DIN 12828 appeared in the spring of 2005 in the Beuth Verlag. The BHKS and the ZVSHK, originated this work together with the DIN in order to facilitate a more clear handling of the standard for a general practitioner. (Order number Beuth Verlag: 15920)


Reflex is working to continue documenting the development of the actual situation here. The documents that have been developed and made available have been edited to the best of our knowledge and belief. We appreciate you contacting us about your experiences and questions about dealing with the standard.






Directive for health and safety requirements for the use of work equipment by workers at work

General, area of applicability, start of the validity

Among other things, the Ordinance on Industrial Safety and Health regulates the required measures for and with the operation of systems that require monitoring. This is understood to also mean (in terms of the ordinance), for example, pressure equipment such as diaphragm pressure expansion vessels as well as heat exchangers. The manufacture and marketing of such equipment is already harmonized and regulated in Europe since 1997 in the Pressure Equipment Directive 97/23/EC and has been used accordingly since then. Reflex supplies the market with equipment that has been constructed, inspected, and CE-labeled according to this directive.

The well-known pressure vessel ordinance (DruckbehV) and steam boiler ordinance (DampfkV) were available up to now as basis for monitoring the operation of systems. However, they were not in harmony with the directive 97/23/EC. Surprising to many, on January 1, 2003, the Ordinance on Industrial Safety and Health (BetrSichV) came into force, which was European harmonized and applicable as national German law. This suspended or replaced (among others) the steam boiler and pressure vessel ordinances. The basis of the BetrSichV German Product and Equipment Safety Act (GPSG) and thus the Occupational Health and Safety Code.


(in the period of application up until December 31, 2004) 

Those who knew the DruckbehV well will not superficially notice any large difference to the BetrSichV in reference to the diaphragm pressure expansion vessels requiring monitoring. However, diaphragm pressure expansion vessels in heating systems with STB setting temperatures up to 120°C did have a general special status in the DruckbehV.

Recurring inspections and their deadlines were able to be determined by the operators themselves. This regulation was dropped after the commencement of the BetrSichV on January 1, 2003 and was applicable at most only for "small" diaphragm pressure expansion vessels. Commissioning and recurring inspections in heating systems had to also be performed by the approved monitoring points (ZÜS, until further notice of the TÜV) in consideration of the maximum deadlines for a host of diaphragm pressure expansion vessels. However, as of January 1, 2005 there are simplified rules which are strongly adapted to the earlier procedures through the DruckbehV.  

(in the period of application as of January 1, 2005)

Since the BetrSichV means an enormous tightening of the DruckbehV for diaphragm pressure expansion vessels and heating systems and in no case should have been the objective of the BetrSichV, a modified ordinance in this point came into force at the beginning of the year.

The following now applies:

Indirectly heated heat exchangers and expansion vessels in heating and cooling systems with water temperatures of a maximum of 120 C can be inspected before commissioning and recurrently by a qualified person (bP). The inspections are to be arranged by the operator.

(Note: Cooling systems are now expressly included in this special observation compared with the DruckbehV.)

Diaphragm pressure expansion vessels in water supply systems are not affected by this simplification.

The classification and assignment of the corresponding requirements occurs in dependence on the product from container volumes [l] and the maximum possible system pressure [bar] (often the safety valve activation pressure).



VDI 2035, Part 1 - "Prevention of damage in water heating installations – scale formation in water heating systems"

Area of applicability:

Hot-water heating systems according to DIN EN 12828, Potable water systems according to DIN 4753 

General Information

With the 5th edition, the VDI 2035 Part 1 completes the update of the long-known directive. A revision, with focus on the determination of new recommendations for filling and make-up water in domestic hot water installations appeared to be necessary. This is also the substance of the following information. In addition, the directive also includes information about systems for the heating of potable water, however, this is not discussed here.

The background for the changed requirements for filling and make-up water in heating systems is the fact that the heat generators continue to become more compact while providing increased heating performance. Likewise, the trend to multi-boiler systems or the trend to the division of required heating performance onto multiple heat generators or even to modularly switched units is unmistakable.

Due to construction, the generator heat surface is correspondingly loaded more which means it is even more important that the heat dissipation be possible without hindrance. Any reduction of the heat flow is to be prevented, and thus the application of VDI 2035 Part 1 is obvious, particularly with regard to scale formation. It is supplemented by Part 2, water-side corrosion (09/1998), and Part 3 exhaust-side corrosion (9/2000).

What is important or what has changed?

Water Treatment

The amount of the regional water hardness is decisive for the decision as to whether measures for the prevention of boiler scale need to be taken. Moreover, the size of the heating system determines the limit values that are to be complied with. If necessary, these limit values are to be realized by technical measures. In areas with medium to hard water hardness, looking at the specifications of the directive is recommended.

The directive attempts to create a practical foundation which results in a catalog of measures which are simple to apply. There are now limit values for the maximum water hardness to be utilized by heat generators for all power ranges. Requirements are also placed on the smallest units, provided these deal with circulating water heaters (performance specification boiler water content Vk<0.3 l/kW) or systems with electric heating elements (e.g. heat pumps). In principle, one can assume that all wall-mounted heat generators, be they condensing boilers, or heat value generators, but also heat pumps with electric emergency heating fall into this category. The following table shows the limit values of the water hardness based on the total power of the heat generator modeled after the texts of the directive:

However, column 3 of the table only applies if the specific water content of the complete system is < 20 l/kW based on the smallest heat generator output (for multi-boiler systems). With the knowledge that a system with compact radiators and a design temperature of 70/50 °C has approx. 11 l/kW specific water content, this limit is already exceeded with a two-boiler system and a power distribution of 50/50 %. Because based on one boiler, a specific system content of 22 l/kW would already result.

In this case, the requirements of the next higher power level of the table are already decisive (column 4). The use of hot-water buffer tanks has an additional massive influence on the characteristic value of the specific water content. In this context, a significant amount of water to be heated comes into play, which must be taken into account.

A softening to nearly 0°dH is required (column 5) when larger amounts of make-up water for the system are to be expected (> 3 times Va per lifecycle of the system) or if the specific water content is > 50 l/kW.

Constructive measures

To keep the quantity of a water change as low as possible, e.g. during partial repairs, sectional shut-offs are to be utilized. For systems > 50 kW, a water meter is to be provided in the make-up water feedline. For circulating water heaters and a water


For the protection and preservation of an effective heat generation, the new VDI 2035 Part 1 (as a result of the latest experiences) supports the requirements of many heat generator manufacturers to minimize calcifications, particularly in the boiler. This is surely done in the interests of all manufacturers, planners, technicians, and operators.

What is important is the understanding that there are specified parameters and recommendations down to even the smallest units, parameters which are to be complied with, so as not to immediately stumble here in the event of damage. Provided you have familiarized yourself with the regional conditions with regard to the existing water harnesses, you will quickly find the necessary measures that need to be initiated. For the area of applicability of the VDI 2035 Part 1, the water softening by means of ion exchange resin is the most simple version to the implemented.




VDI 2035, Part 2 - "Prevention of damage in water heating installations – water-side corrosion"

Area of applicability: 

Hot-water heating systems according to DIN EN 12828,
Potable water systems according to DIN 4753,

General information

Just as the existing revision of Part 1 (already in existence for some time), Part 2 of this directive (which appeared in August) joins the "tradition" of the continuous further development of the VDI 2035.

With the objective of protecting the components of heating systems in buildings in an effective way, Part 2 has the same handwriting as Part 1 and is useful to the practitioner as a valuable orientation. Current and up-to-date knowledge of the system technology, the applied materials and new knowledge about corrosion procedures and their interrelation have been the basis and the background for the revision of this part.

With practical, well summarize information, Part 2 has the intention of protecting components of heating systems from destruction or corrosion attack or minimizing the probability of corrosion.

What is important or what has changed?

Anti-corrosive closed system

 The essence of Part 2 is the finding that a main aspect for the prevention of corrosion is that there must be consistent prevention of continually introduced oxygen into the heating water. Great importance is attached here to the pressurization. This is not surprising, however, it is described here in clarity for the first time in a directive outside of the large system technology.

The directive requires the construction of anti-corrosion closed systems and "kicks" system components that bring heating water into direct contact with atmospheric oxygen "off the field". Because of this, pressurization systems with expansion vessels without diaphragms, for example, are now finally and clearly emerging in light of corrosion investigations in a way that is understandable for everyone.

Maintenance with focus on pressurization

 Likewise, the long known aspect of the necessary maintenance is also brought into focus by expansion vessels. When they are not maintained or inoperative, they cause vacuum formation in the system and thus promote the entry of air – with the well-known consequences.

Professional planning

is also required with the information that has existed in DIN EN 12828 for many years. Proper planning is an elementary foundation for the prevention of damage.

No chemicals

 Anti-corrosion procedures in conjunction with different materials are very clearly described for the practitioner. The VDI continuously and clearly indicates that the "chemical bomb" in the form of additives must or should only be used in the most seldom of cases. The VDI advocates precisely the opposite thus clearing up the jungle of water chemistry in heating systems.


Importantly high value is placed on the awareness and monitoring of the ph-value. Depending on the materials used, it should lie between 8.2 and 10. The expert will have to get used to the necessity of being aware about the necessary or existing ph-value of the heating water. In addition to the oxygen content, it is an important factor for the possibility of the presence of corrosion processes.

The ph-value is simple to check without a large amount of technical expenditure. Systems require a certain amount of time for the development of or stabilization of the ph-value of the heating water. Usually, no external assistance is necessary in order to adjust the required alkaline range. The so-called inherent alkaline treatment takes place on its own after the system is filled and should be checked after 8 to 12 weeks of operating time.

New - the electrical conductivity

The observation of the electrical conductivity of the heating water is new in the revision compared to earlier editions. References made to the interrelation already made in other rules about the "low conductivity minimizing the probability of corrosion by oxygen".

Particularly interesting and important in practice is, however, also the information about the fact that additives in the heating water, such as inhibitors or oxygen binders increase the conductivity. I.e. that heating water makes it more conducive for the feared oxygen corrosion. On the topic of inherent alkaline treatment specifically, however, the VDI also explains to the practitioner that in a anti-corrosion closed system uncritical concentrations of oxygen will adjust on their own.

Against a misinterpretation, as already mentioned numerous times in publications, that a secure system operation is only possible with low-salt (desalinated) heating water is to be warned about at this juncture.


The VDI 2035 suggests the use of a system book for the safety of the system creator and naturally for the operator. As already clearly required in Part 1, and important for the overview to the provided measures, the system book should document which measures are necessary or were performed. The system book is structured as model example and summarizes all important parameters of both parts of the directive once more.


The VDI 2035 Part 2 offers the professional good and clear information about the prevention of corrosion damage and heating systems. The information is displayed in a way that allows the interested professional to understand it and implement it. The most important principles are clearly presented in detail and the VDI is not afraid of making critical comments about chemistry. In all cases, it serves to create clarity in dealing with heating water treatment and preparation.

With this directive, the VDI has again made a work available for the professional which, in contrast to the predominantly European body of standards, is to be applied very specifically.