Brand: Deks Ventilation

Introduction The Selkirk Twin Wall chimney system is designed for use with oil, gas and solid fuel w...

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The Selkirk Twin Wall chimney system is designed for use with oil, gas and solid fuel when used with the appropriate fire stopping components. The system is designed for gravity flow application. The Selkirk Twin Wall chimney system is available in a range of diameters and this brochure relates to the 127mm (5”) – 203mm (8”) range. The system consists of straight lengths and fittings which are constructed entirely from stainless steel and a 25mm (1”) insulated annulus. The external skin is manufactured from 304 grade matt finish stainless steel and carries the structural load, and the inner liner is resistant to the often corrosive products of combustion, and is free to expand or contract as flue gas temperatures change. The 316 grade inner liner heats rapidly to produce a strong draught which ensures that waste gases are exhausted and condensation of the harmful products of combustion is minimised. The system can be used internally or externally. The relatively low external wall temperature permits installation with only a 50mm (2”) air gap clearance to combustible materials.

Composition Lengths and fittings are twin-walled with a 25mm (1”) cavity. The outer casing is joined to both male and female couplers, while the inner liner is connected only to the male coupler, as flue gas temperatures vary the inner liner can expand and contract without affecting the structural performance. Selkirk Twin Wall chimney is insulated with rockwool and this high quality insulation has an optimum and carefully controlled density which maintains a relatively high flue gas temperature throughout the chimney lengths. Lengths and fittings are twist-locked together with a one eighth turn. Locking bands fit over the two rolled seams at joints between lengths and fittings and MUST be used.


Lengths and fittings are designed to be installed with the male coupling uppermost. Joints are achieved by placing the female coupling over the male coupling and making a one-eighth turn. A Locking band must be used to secure every joint and to ensure a firm connection.

Connecting to the appliance

The Adaptor is designed to make the connection to the appliance flue gas outlet or to a section of flue pipe to building regulation requirements.


The weight of the chimney may be carried by a number of different support components depending on whether the chimney is installed internally or externally, and whether it is supported by the roof, ceiling, floor or external wall. These components include the Wall Support, Ceiling Support and Roof Support. Lateral stability is provided by Wall Bands.

Supporting free-standing chimneys

Where the chimney exceeds 1.5 metres (4.9ft) beyond the last support it must be braced with a roof brace kit or similar. The bracket should be fitted above a locking band and as close to the joint as possible.

Roof Support

The Roof Support is designed to support the chimney on the roof timbers and is provided with adjustable gimbal plates.


The relatively low external casing temperature experienced in normal operation permits installation with only 50mm air gap clearance to combustible materials. Where the Twin-Wall Chimney passes through a combustible floor the appropriate firestopping components must be used.

Lengths of Chimney

Standard lengths of 1219mm, 914mm, 610mm, 457mm, 305mm and 152mm and an adjustable length are available. Individual tables provide details.


Building regulations stipulate that where bends are essential, they should be angled at no more than 45° to the vertical. 15°, 30° and 45° elbows are available.

Floor and Ceiling Penetration

Where the chimney penetrates a combustible floor or ceiling a 50mm air gap clearance must be maintained from the outer skin of the chimney to any combustible materials. Components are available which cater for such requirements. Please refer to floor penetration requirements at the rear of this brochure

Roof Penetrations

Where the chimney penetrates the roof an appropriate flashing should be used. The Seldek range of flashings is specifically designed for this purpose. To fit, trim the E.P.D.M. cone to suit the external pipe size using sharp tin snips or scissors, slide down pipe using water as a lubricant. Dress the aluminium or lead base over the profile of the tiles. Providing the cone has been cut to the appropriate size, the use of a storm collar or sealant is not required. If the chimney has a raised seam on the outer skin a small amount of silicone sealant should be applied where the chimney penetrates the E.P.D.M. cone of the flashing.


Two types of terminations are available. Both have female couplers and are fixed to the top chimney length and secured with a locking band. The rain cap is a domed stainless steel cap. The AD cowl provides aerodynamic down-draught protection. Both terminations are deemed to be sacrificial components.