Why does discolouration occur in the area around the chimney top of my stainless steel chimney?

In some cases, tarnish may occur at the chimney top of the stainless steel chimney. This occurs especially when the hot exhaust gases (temperatures usually > 250 ° C) are blown by wind to the outer shell. The superficial discolouration normally has no effect on corrosion resistance when completely removed.

The colourings occurring after soot fire can very often be attributed to high temperatures, which are responsible for the wearing out of the stainless steel and, therefore, in most cases it must be assumed that corrosion can occur.

How can tarnish colours be removed?

As the tarnish colours are mostly just discolorations of the surface, they can usually be easily removed. This can be done by any best commercially available glass cleaner.

Which types of wood are suitable as fuel?

The 1st BImSchV contains a list of all the fuels that you are allowed to use in a small combustion plant. The following box lists the types of wood allowed in households.

In addition, the information provided by the equipment manufacturer regarding suitable fuels must be respected.

Wood fuels approved for incineration in households are (§ 3 Para. (1) of 1st BImSchV):

- barbecue charcoal, barbecue charcoal briquettes according to DIN EN 1860, September 2005 edition,

- untreated lumpy wood including adherent bark, for example in the form of logs, wood chips, as well as brushwood and cones,

- untreated natural wood, for example in the form of sawdust, shavings, grinding dust or bark ²,

- Pressings of natural wood in the form of wood briquettes according to DIN 51731, October 1996 edition, or in the form of wood pellets in accordance with the fuel-technical requirements of the DINplus certification program "wood pellets for use in small fireplaces according to DIN 51731-HP 5", August 2007 edition, or others Wood pellets of natural wood of equivalent quality.


² This fuel may only be used by wood processing companies where it is waste.

What should be considered for low-energy houses?

Low-energy and passive houses must meet increased demands on the leak tightness of the building, therefore, the selection of suitable fireplaces and exhaust systems is of significant importance.

Here, first and foremost, care should be taken to use systems that have been tested for room-air-independent operation, since room-air-dependent fireplaces can, on the one hand, lead to an unwanted cooling of the living space as a result of using the room air and, on the other hand, it can happen that that such a system, due to the dense building shell, does not work, since only a small amount of fresh air can flow through the very low air exchange rate and thus safe operation of the fireplace is not guaranteed.


Environmental regulations / fine dust regulation

The first German Federal Immission Control Ordinance, which has been in force since 22.03.2010 in Germany (1st BimSchV), set the limit values for pollutant emissions of small and medium-sized combustion plants.

In particular, the limit values for dust and carbon monoxide for new fireplaces with solid fuels (wood, etc.) were significantly tightened. Since 01.01.2015, only single fireplaces (e.g. stoves) may be installed, which fulfil the requirements of Stage 2 of the 1st BimSchV. The same applies to central solid fuel stoves (e.g. woodchip heating). Newly constructed fireplaces for firewood must comply with these limits from 01.01.2017.

In addition, discharge conditions were specified which set requirements for the position of the chimney outlet. More: How high must be the chimney?


Which materials can be used for exhaust systems?

For exhaust systems, a wide variety of materials can be used. Here, in addition to the classic bricks for single wall construction, modern double wall or triple wall system exhaust systems are also available. This consists usually of an inner pipe of stainless steel or ceramic, an insulating layer, which counteracts a strong cooling of the exhaust gases, and an outer shell made of stainless steel (classic stainless steel chimney), lightweight concrete or various approved fire protection materials for lightweight shafts (e.g. calcium silicate, vermiculite, aerated concrete).

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