Calorific value - which chimney fits?


After replacing an old dilapidated heating system with a new modern condensing boiler, the cross section of the old chimney usually ceases to be right and needs to be replaced with a completely new chimney or special piping.

Chimney too big for new heating

In most cases, the cross section of the old chimney is too large to meet the new requirements. Then the cross-section must be reduced.

Resistant to moisture

Since the new heating with condensing technology sends more water than heat through the chimney, the chimney must be moisture resistant. Of course these are not the most old stone chimneys.

Important for the calculation of the chimney

These points are important for the calculation of the cross section and material for the new chimney with a condensing heater.

  • Power of heating in kW
  • Height of the previous chimney
  • how many heaters are operated on a chimney
  • the type of the respective condensing heating
  • Exhaust system and pressure ratio

Brennwert chimney to standard

To calculate the correct diameter for a chimney with condensing technology, the EU standard DIN EN 13384-1 is used, if it is a single fireplace. If it concerns several fireplaces with condensing technology at a chimney, the DIN EN 13384-2 applies.

Cooler exhaust air by calorific value

A condensing boiler works with a much lower power, so it not only saves oil or gas, it also saves a lot on the waste heat. Therefore, the waste heat conducted through the chimney is rather humid than warm.

Cooler air also gets much heavier than warm air does. Above all, if the diameter of the chimney is too large, the exhaust gases of the heater can not be dissipated. So does the heater itself damage.

Tips & Tricks

Depending on the heating system with condensing technology, you can either have a plastic pipe in the old chimney or the chimney is narrowed by a new stainless steel pipe. Although plastic is much cheaper, depending on the system, it will not be as durable, so stainless steel is piping often better.


Video Board: Firewood Moisture Testing