A steam boiler with an economiser and an exhaust temperature of 150°C requires a flue draught of at least 5Pa. A flue gas temperature of 65°C requires a flue draught of 1 Pa.

The advantages for you

  • Double-walled stainless steel chimneys – no rust
  • 25 mm insulation – low heat loss resulting in more even draught
  • Plug-in system – easy to install
  • Extensive range of moulded parts as standard – no expensive special parts necessary
  • Sealed connections – sealed against short-term excess pressure
  • JUMAG will gladly perform chimney calculations
  • Sketches for the chimney constructor available upon request
  • We provide you with everything you need

How it works – correct chimney length

A too-short chimney has the following risks:

  • The chimney does not draw sufficiently and there is a pressure in the chimney. Flue gas may flow undefinedly into the environment from the chimney transfers because of this.
  • Heat in the boiler rises up and the burner installed there can be damaged if cooling is insufficient due to lack of flue draught.

A too-long chimney has the following risks:

  • In standstill, the chimney will draw unnecessary amounts of fresh air through the steam boiler and cool it off.
  • Long chimneys are accordingly more expensive and may need elaborate catching constructions.

Therefore, it is important to choose the proper chimney length. No overpressure may build up in the chimney during burner operation. Therefore, a flue draught is necessary. The burner blower pushes the flue gases to the chimney. Standstill is more critical than operation; there must be enough draught to protect the burner from rising heat.

About us

For more than 40 years, we have been developing, producing and selling oil and gas-fired steam boilers.

JUMAG steam systems represent efficiency and user-friendliness.


Jumag Dampferzeuger GmbH
Badener Str. 8a
69493 Hirschberg

+49 6201 84603-0



We are happy to advise you