Grün Engineering
Two stainless twin wall flue risers on cantilever brackets up the rear wall of a school building
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Flagship project Boiler flues GE4026

Walthamstow Academy

Eight boilers in two banks, routed out of a crowded plantroom to two external twin wall risers.

Site
Walthamstow Academy
Town
London, London
Sector
Education
Status
Complete

Key facts

boilers, 150 kW each, in two banks of four
8
headers inside, twin wall risers outside
Ø250
of flue: 32 m twin wall, 23.5 m single wall
55.5 m
risers, each with a 60° offset round the eaves
2
from CCTV survey to installation
7 weeks

The challenge

The customer expected to reuse the existing riser.

Our CCTV survey found screws and rivets through its liner, and condensate staining.

The plantroom was already full of services, so any new route had to thread through them and leave the building.

What we did

We designed an external route. Inside, single wall flue takes a Ø100 connection from each boiler into special Ø250 tees, with one header per bank rising at 3° to the wall.

From the wall it is twin wall insulated: through the riser duct, round the building on cantilever brackets and up two risers with base tees and drains.

The rendered panels above the brickwork could not take load, so the main brackets went into the brick and the upper supports into the steel behind the facade.

The outside work was done from a boom MEWP in a fenced compound.

The result

Both flues were smoke tested on completion. The smoke left at the terminals with no visible leakage.

The old internal flues were capped and made safe.

The wall holes came down from the quoted 500 mm to 300 mm and 350 mm once the design was fixed.

On site.

8 photographs. Tap a photo to see it larger.

Walthamstow Academy, London. The two risers, fed by the stacked horizontals on cantilever brackets.
Walthamstow Academy, London. Twin flues rising above the plantroom roof at the back of the building.
Walthamstow Academy, London. The two terminals above the roof edge at dusk.
Walthamstow Academy, London. Two risers on wall brackets up the rendered wall.
Walthamstow Academy, London. A bank of four boilers into its Ø250 header, threaded through the existing services.
Walthamstow Academy, London. Header and branches at high level above the boilers.
Walthamstow Academy, London. Header and connections above the boilers.
Survey photo. Walthamstow Academy, London. CCTV still of the old riser: screws through the liner.

The drawing.

From our 3D model.

Labelled isometric drawing of eight boilers, two single wall headers and two external twin wall risers with a 60 degree offset
Isometric from our 3D model, built off drawing W2 and the completion photos.

Finishing details

The details we leave behind.

  • Base tees and stacked horizontal flues on strut channel frames off a brick wall

    Base tees and drains

    A base tee with cap and drain at the foot of each riser. Condensate drains left ready for connection.

  • Flue risers held on wall brackets

    Braced cantilevers

    Five cantilever bracket assemblies in the brickwork, tied together up the full height of the risers.

  • Two flue terminals above a roof edge

    Offset round the eaves

    A 60° offset takes each riser past the soffit to terminal height.

  • Old riser made safe

    The existing internal flues were capped and made safe once the new system was in.

Handover

What the client got.

The documents on record for this job. Handover documents normally go into the customer's project folder before the engineers get home.

  • CCTV surveyOf the existing riser, 3 October 2025
  • Design and drawingDrawing W2 and builders' work schedule
  • Job-specific RAMS
  • Daily progress reportsWith photos, 22 and 24 November 2025
  • Smoke test recordTwo flues, recorded on completion
  • O&M and certificationAt handover

Related services

Boiler flues Testing and surveys Steelwork and supports Design and calculations

Short job records: GE4026.

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