The Dunbrik Triple Seven gas flue block system enables a builder to incorporate a gas flue in a timber frame house without the expense of having a separate chimney. This system is based on the Mini Clearflow gas flue block system with the addition of flanking blocks and steel U channel to support the flue within the timber frame while allowing for shrinkage of the timber frame. Gas fires suitable for pre-cast flues may be fitted - these are Class two gas fires which are usually under 7kW input and include efficient live fuel effect gas fires.

Two sizes of recess opening are available to suit different fire sizes and chimney breast arrangements. The flue outlet depends upon the house design. It is usually through twin-wall flue pipe to a ridge vent or to a gas terminal at eaves or through the roof slope. Alternatively a traditional chimney stack can be built at eaves or gable/party wall.

The gas flue blocks are bonded with the special flanking blocks into the vertical steel U channel. This can be in an outer wall, a party wall or partition wall. In many cases there is no chimney breast intruding into the living area.

The gas flue blocks are designed for ease of installation. The tongue and socket detail provides 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 have made flues for timber frame houses for 20 years and the current system introduced in 1996 is installed in over 1000 houses annually.