What is VDI2035, and why do I need it?

VDI2035 is a set of water quality guidelines for heating water developed in 2009 by the Association of German Engineers. The equivalent in the UK would be BS7593; however, it is widely accepted that the VDI2035 is based on stronger scientific evidence and is much more in-depth. Compared to the VDI2035, the UK’s equivalent set of regulations for heating water is quite brief and vague, which many engineers argue leads to an inability to interpret or follow proper health and safety guidelines. In addition, the VDI2035 is recognised as a set of corrosion preventative measures within water-heating systems. In contrast, the methods commonly employed in the UK are typically a reaction to existing corrosion and use potentially harmful and unnecessary chemical inhibitors.

What is included in the VDI2035?

There are three important parts to the VDI2035, outlined below:

Part 1: Scale Formation in Drinking water and Water Heating System

Scaling occurs within plumbing systems when the water has particularly high levels of minerals like calcium carbonates, which over time build up on the surfaces of your pipes and cause long-term damage to your pipes and boiler. Problems that can occur due to scaling may include the reduced efficiency of your boiler, reduced or blocked flow to your fixtures or appliances, and leaky valves.

To prevent the formation of scaling within your pipes, it is important that the hardness of your water is below 200ppm of mineral concentration. Part 1 of VDI2035 recommends a comprehensive demineralisation of the fill water for a closed water heating system.

Part 2: Waterside Corrosion

Waterside corrosion happens to a water heating system, such as your boiler, when high temperatures cause oxygen and acid to dissolve in the water. If uncontrolled, waterside corrosion can lead to severe pitting, pinholing, and embrittling of the tube metal and will eventually lead to the breakdown of your water heating system.

Part 2 of VDI2035 is designed for systems where the flow temperature of the water is less than 1000 C˚ and where, over the service life of a system, the volume of make-up water will not be more than three times the volume of the initial make-up water. This part recommends a professional planned system in which oxygen corrosion is prevented without using chemicals during the operation of the water heating system. Part 2 of the VDI2035 highlights that oxygen levels can be reduced and maintained at a low level by the correct start-up of a plant, decoration, correct pressure maintenance, and the design of a system preventing oxygen ingress.

This section also highlights that inhibitors (chemicals used to protect the lifespan of your heating system) should only be used as corrosive protection in water heating systems when oxygen diffusion is expected. These inhibitors should be regularly checked according to the manufacturer’s specifications.

Part 3: Corrosion by Flue Gases

Flue gases are produced by the combustion of fuels containing contaminates that can condense into sulfuric, sulphurous, or hydrochloric acid droplets. The best way to prevent flue gas corrosion is to use more resistant material and reduce the number of contaminants in heater and boiler fuels.

Part 3 of the VDI2035 focuses on the gas-related corrosion of metallic materials within a hot water heating system. This section specifically refers to the exhaust gas or flue gas system and is unrelated to system filling and water treatment. Although the VDI2035 does not cover this part extensively, it assumes that heating systems will follow previous regulations (specifically DIN EN 14336: 2005-01 and DIN EN 14868-2005), which states that heating system must be flushed and cleaned before the installation and usage of a water-based heating system.

Is the VDI2035 only used in Germany?

Austria and Switzerland have developed similar regulations, HöNORM IN 5195-1 and SWKI BT201-01, respectively. All these water policy standards recommend the non-use of inhibitors. In many countries worldwide, hot-water boilers use alkaline chemicals for water treatment to prevent corrosion and fouling inside heating systems. However, depending on the type of pipes used, such as copper or aluminium, chemical reactions could be very serious under alkaline water conditions. Depending on the heating systems, the use of inhibitors can become very complicated, hence moving away from their usage in several European countries.

It is also important to note that while many European appliance manufacturers base their own water treatment guidance on the VDI2035, this water treatment standard is not a recognised guideline in the UK. Consequently, there is a concern by many UK-based water and heating specialists that the recommendations developed in the VDI2035 may not be suited for UK systems.

However, since the VDI2035 is considered a corrosion preventative system, compared to a reactionary one commonly used in the UK, there is no doubt that it is far more effective, less costly in the long-term, and significantly more effective environmentally friendly.

Why is the VDI2035 an important standard in water heating?

Many chemical engineers, particularly water and heating specialists, have come to accept that the use of chemicals for corrosion inhibitors inside of water heating boilers has become unnecessary to prevent malfunction and system corrosion.

The VDI2035 was created using strong scientific evidence to develop a water-heating system in which corrosion, blockages, scale, and damage to pumps, seal and gaskets is unlikely. The methods recommended in the VDI2035 are based on natural science rather than the use of unnecessary and potentially harmful chemicals.

Why do I need the VDI2035?

Ultimately, the guidelines developed in the VDI2035 have helped to significantly reduce the damage caused in traditional water heating systems, which has been shown to reduce the lifespan of expensive equipment. By following the guidelines recommended in the VDI2035, a water heating system becomes much more environmentally friendly, eliminating the use of unnecessary chemicals and the need for regular equipment replacement. This system will ultimately save your clients a lot of stress and money through lower heating bills and a reduction in the need to regularly maintain their boiling system.