Flue systems for gas fires

Suitable for:

Dunbrik Mini Clearflow Gas Flue Block System

This is a neat efficient method of providing a flue in a new domestic dwelling. Gas fires suitable for “pre-cast flues” may be fitted. The outlet depends upon the house design. It is usually through twinwall flue pipe in the roof space to a ridge vent or to a gas terminal at eaves or through the roof slope.

The gas flue blocks are built and bonded into the inner leaf blockwork of an external wall, into a party wall or partition wall.

The gas flue blocks are designed for ease of installation. The tongue and socket detail provide a tight concrete-to-concrete internal joint and an external compressive seal using special heat resistant sealant. The bonding nib has a 10mm cut-out for mortar jointing with the adjacent blockwork – this assists coursing.

Dunbrik Triple 7

Gas flue block fittings for timber framed houses. The Triple 7 Panel fittings have been designed to allow the Mini Clearflow gas flue block system to be installed within the inner leaf of a Timber Frame construction by using specially designed flanking blocks and fixing channels. The system is also suitable for other forms of modular build.

System details and design guidance

The Dunbrik A1 Concrete Flue Liner Systems are used in the construction of domestic chimneys suitable for all types of domestic fires. A domestic chimney is a structure made with a minimum of 100mm thick masonry lined with purpose made flue liners. Householders can burn any domestic fuel including coal and properly seasoned wood or install any domestic gas fire including flame effect fires.

Flue Liners

Dunbrik concrete liners are made with tongue and socket joints for accurate location and tight jointing. They are manufactured from kiln burnt aggregate and Portland cement and are designed to withstand repeated temperature fluctuations.

Flue liners should be joined with Dunseal fire proof mortar paste. Allow approximately 3 joints per cartridge for 200mm liners, 2 joints for 250mm & 300mm liners and 1 joint for 450mm liners. Any void between flue liners and masonry surround should be filled with Dunfil insulating infill.

Liner Standards

British Standard BS EN 1857 established performance standards for concrete flue liners for domestic chimneys.

Dunbrik liners have been tested by BSRIA and achieved the highest categories in each class as follows:

Dunbrik Type A1 – T600 N1 G D 3

Performance Data

  • T600 – Temperature nominal operating temperature 600°C
  • N1 – Gas tightness negative pressure test at 40 Pascal
  • G – Sootfire resistance heat shock tested to 1,000°C for 30 minutes
  • D – Condensate resistance for dry flue conditions
  • 3 – Corrosion resistance for all domestic fuels (scrub test for durability)


UK Building Regulations ADJ

Dunbrik A1 Concrete Flue Liners meet the minimum standards set in approved document J (ADJ) and exceed the requirements for temperature and gas tightness.

Red set wide recess starter block (3 per flue)

Red set wide gather block

M set deep & wide recess starter block (3 per flue)

M set deep & wide gatherblock

Dense backup block 100mm

Straight bonded gas flue block 225mm

Straight bonded gas flue block 150mm

Straight bonded gas flue block 75mm

95mm Lateral offset block gas flue

35mm Backset gas flue block

25mm Backset gas flue block

125mm Backset gas flue block

Double tongue flue block 190mm

Gas flue block without bonding nib 225mm

Gas flue block without bonding nib 150mm

Gas flue block without bonding nib 75mm

Top exit gas flue transfer block

Top exit block with connector pipe

Side exit gas flue transfer block

Side exit block with connector pipe

Small flue flanking block

Large flue flanking block

Angled exit flanking block

Top exit flanking block

Recess unit flanking block

Top sealing lintel

Recess unit flanking block

Steel U Channel 1250mm

Flue block connector/adaptor

457mm (18″) adjustable length

Wall band 56mm spacer

Flue pipe 1524mm (60″)

Flue pipe 914mm (36″)

Flue pipe 457mm (18″)

Flue pipe 305mm (12″)

Flue pipe 152mm (6″)

0° to 90° adjustable bend

Adjustable wall bracket

Adjustable flashing 5° to 30° pitch

Adjustable flashing 32° to 45° pitch

Storm collar and sealant

Gas vent terminal

Ridge tile adaptor (gasket not supplied)

Gas flue box – Free standing

Support plate and flange

Firestop spacer plate

Blakbord insulation panel

Flue block silicone sealant 310ml cartridge

Smoke pellets – 6 per tube

Flue notice plate

Topguard steel cowl (red or buff)

Cannon head chimney pot (red or buff)

Cannon head chimney pot (red or buff) 300mm

Stellgas terminal – pot insert

Gastyle II segmental – third round

Gastyle II half round

Gastyle II angled – 30 degree pitch