NVS Limited

Selkirk IL Flue (Insta Lock) Description and Installation



All lengths and fittings have been designed to be installed with the male coupling uppermost. The female coupling of the next component is pushed and twisted into place, providing a firm and secure connection by a simple locking device and a lock tab for added security.


Wall bands are available and for wall fixed installations should be used at 3m (10ft) centres. The wall bands give a nominal 50mm (2") clearance to the wall and they provide lateral support. A support plate is available which provides support for the vent at floor penetrations. The support plate is fixed on top of the floor joists and the flanged collar is clamped around the flue. The flange rests on the plate. A firestop plate is used on the underside of the ceiling penetration. Both these components provide a 25mm air gap clearance from combustibles. Where the gas vent extends more than 1m above the last support (not including the terminal), it must be braced.

Lengths of Vent

Lengths are available from 152mm (6") to 1523mm (60") and should be used in combination to achieve the required height. Gas vent lengths should not be cut. Adjustable lengths are available to accommodate odd distances between vent lengths or connectors. To accommodate the required length, these telescope over any standard length. The installed length of each unit is 38mm (1 - 1/22) less than the overall length.


Terminating components include a fabricated aluminium gas vent terminal, a round top and a ridge tile adaptor.

Structure and Manufacturer

All lengths and fittings are manufactured with the inner liner fabricated from aluminium. The outer casing is zalutite. Vertical seams are rolled and securely locked. The inner and outer casings are joined at one end only and a 6mm (1/4") air gap is incorporated: the inner liner is therefore free to expand as the temperature changes in the flue. The various components are joined by a simple swaged locking joint and a lock tab if desired.

Selkirk Insta-Lock Gas Vent LOCKTAB feature

The LOCKTAB feature was developed in response to feedback concerning the use of sheet metal screws to secure GAS VENT sections. In many areas, the use of sheet metal screws is either a commonly accepted practice or a local requirement. The use of 1/4" sheet metal screws is expensive and time-consuming for installers. The use of the LOCKTAB feature gives installers the option of engaging this tab instead of using sheet metal screws. Selkirk Insta Lock is a factory made twin wall gas vent system comprising a range of straight lengths, associated fittings and accessories.

It is manufactured with an aluminium liner and an outer casing of Zalutite. The air gap between the outer casing and inner liner insulates the vent and ensures a strong draft at the start of firing in order to minimize condensation. The resulting low external temperature under normal operating conditions permits installation with only 25mm (1 in.) clearance to combustible materials. Lengths and fittings lock together to provide a rigid flue system and to ensure maximum ease of site assembly. The unique lock tab feature further secures each joint.


The Selkirk Insta Lock Gas Vent system must be installed in accordance with the requirements of BS5440 Part 1 code of practice for flues and air supply for gas appliances of rated input not exceeding 60KW, the requirements of approved document J of D.O.E building regulations and Section F of the building standards (Scotland) Regulations. The Insta Lock system is manufactured and tested to comply with BS715 1993 and complies with EN1856 Part 1 when tested in accordance with BSEN 1859. Product designation T250N2DVmL1100300(25) Certificate No. 0086CPD-50308.

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