Heating water according to VDI 2035

Heating water requirements

Properly treat heating water according to German standard

Who is the VDI?

Verein Deutscher Ingenieure (VDI) (English: Association of German Engineers) is an organization with over 150,000 engineers and natural scientists. More than 12,000 honorary experts process the latest findings every year to promote the technology location. Established in 1856, the VDI is today the largest engineering association in Western Europe. The role of the VDI in Germany is comparable to that of the American Society of Civil Engineers (ASCE) in the United States or Engineers Australia (EA) in Australia barring the broader field of work of the VDI. The VDI is not a union. The association promotes the advancement of technology and represents the interests of engineers and of engineering businesses in Germany.

Source: wikipedia

Theory and practice

Theory and practice

If the heating is properly filled, no deposits can form and the corrosion is reduced to a minimum. Should damage nevertheless occur, there are various reasons. The causes of heating damage can be: Too much oxygen in the water, mud has formed or/and the ph is in the acidic range.

But what does "properly filled" mean?

The VDI guideline published by the Association of German Engineers (VDI)2035 places demands on the fill water, both the scale formation as well as (the oxygen as well) affect electrical conductivity. A Pure water softening is therefore not sufficient.

Which parameters should therefore be considered?

electric conductivity at 25° CµS/cm< 100
german hardness at 25° C°dH< 3
pH value at 25 ° C 8,2 - 10 / 8,2 - 9,0 (aluminium)

These values we reach only by Demineralization

So how is the optimal process going? 

Step 1: Analysis of the heating water

Guide values for the heating water (german standard - VDI 2035) :

  • Electric conductivity: < 100 µS
  • pH-Value: 8,2 - 10 pH (8,2 - 8,5 Aluminium) 
  • Total Hardness: <3°dH

These parameters should be measured using measuring devices. If these values are not given, measures must be taken after the next steps

Step 2: Cleaning the System*

Fill in cleaner and leave it in there for at least one week. Skip this step if corrosion products can be flushed out.

New since 2020: Existing systems often have to deal with silting and magnetite deposits. To remove these, the heating engineer often only has the option of rinsing the system several times and completely changing the fill water. This complex process primarily takes time. In addition, despite multiple flushing, there is always some dirt left in the pipes. The new mobile filter station from magnetic, with which dirt is filtered out of the system water, offers a reliable and clean alternative.


*Step 1&2 are not nescessary if system is filled for the first time

Step 3: Flushing the system

Since the heating purging should take place in individual, separate sections, each must have its own emptying device. Likewise, each section should also have a suitable filling device. If a section has been cleaned sufficiently, it is recommended to shut it off. When the last rinsing process is complete, the entire system should be treated with clear water and special cleaning agents. In this way, existing dirt can be removed.

Step 4: Demineralization

Fill system with deminerlised water in case it is a new system or a refilling after cleaning and flushing. Circulation demineralisation in case system water is not too contaminated. To comply with the german standard, we recommend only using demineralized water. Magnetic has developed special tools with which they can easily produce demineralized water

Step 5: Regulate & Top Up

Heating systems should be replenished to maintain the amount of water. Only demineralized water should be used for this. Magnetic also offers special refill stations for this.

For the long-term regulation of the heating water and the reliable prevention of new deposits, the installation of the magnetic heating water regulator is recommended. This not only saves energy, but also reduces the risk of damage caused by corrosion products in control valves and pumps. Especially in heating systems that are open to diffusion and therefore have an increased risk of corrosion, the HWR (heating water regulator) eliminates all causes of corrosion and sludge formation.

Step 6: Analysis again

Values should be <100 μS/ cm and pH around 7. During the following weeks the self-alkalization process will bring the pH up to the desired 8,2-8,5. The pH value and the conductivity of the heating water should be checked again after 6 months to observe the development of the alkalization.


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