Project Description

The Project:

This project involved the design, supply and installation of a single flue system to serve 2 No. Hoval UltraGas 650kW Condensing gas fired boilers within an IBM plant room. The boilers being replaced were 2 No. standard efficiency gas fired appliances connecting into a non-compliant flue dilution system.


Key factors for the design included:

  • Establishing a suitable alternative to the dilution system as it would not be possible to install a compliant system without significant visual impact.
  • Providing a solution that would be acceptable to local planning department.
  • Finding a suitable new flue route to run from sub-ground-level plantroom to atmosphere.
  • Implementing suitable support for flue on a building that incorporates narrow columns between extensive glass façades
  • A single flue to serve both appliances.
  • All Clean Air Act and IGEM/UP/10 guidance to be followed to ensure a compliant system.

Product Specification:

The following product specification was used throughout the project:

  • Primary Connections – Poujoulat Condensor – 316L grade stainless steel continuously welded single wall flue system installed c/w joint seals.
  • Header – Poujoulat Condensor – 316L grade stainless steel continuously welded single wall flue system installed c/w joint seals.
  • Riser – Poujoulat Therminox TI – 316L grade stainless steel continuously welded internal liner/304 grade stainless steel continuously welded outer case twin wall insulated flue system installed c/w joint seals.


The construction of the new flue was sequential, we installed from the appliances up to high level within the plantroom before running into a header and traversing to exit the building. The plant room sections of the system was installed with a constant incline of 3° to allow efficient drainage of condense throughout.

Due to the design of the building, suitable locations for loadbearing support was limited. In addition, the point where the flue emerged from the plantroom was not in line with a column to provide support throughout the route. Coordinating with the scaffold contractor the access was arranged to allow space for the flue to rise and install the supporting mast for the freestanding section.

The supporting mast was installed first, this was designed to fit neatly onto the shaped column from the first floor and extend support to the flue to the roof level.

In accordance with the flue product manufacturers instructions Therminox TI may be installed under tensile loading, therefore the flue was temporarily supported from the base tee area and built up to the loadbearing support at first floor level, from this point the flue was constructed along the remaining route up the mast to termination in the usual compressive loading.

Finally to provide additional support from wind sheer the flue was tied back to the building with a ‘V’ shaped steel frame affixed to the parapet wall.

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