Mandatory requirements

Mandatory requirements on acceptable chimney, flexible liner and appliance combinations.

Building Regulations Document J requires that a flexible flue liner can only be installed completely enclosed inside a masonry chimney. A non masonry enclosure such as timber or plasterboard boxing in is not acceptable.

The type of flue liner permitted depends on the fuel to be used, the type of appliance and the type and year of chimney construction in which it is to be fitted.

Building Regulations Document J, outlines different requirements for relining masonry chimneys built before and after 1st February 1966. This is summarised in the table below.

Re-use of a previously capped or shortened chimney.

The chimney can be reused providing the existing brickwork is inspected to ensure it is in good condition. The chimney can be lined with the appropriate liner, ensuring that the liner is used only inside the stack. Connection to flue pipe - see Fig.1, or to BVent (gas), KVent (kerosene) or ICS (multifuel) system can be made to the appliance/ termination, by using the appropriate connector inside the chimney, and suitably sealed with fire cement. The stack can be extended using ICS, BVent , KVent or ICID depending on the application see Fig.2.

Re-use of a fitted flexible liner when changing the appliance.

Provided the diameter and type of flex is suitable for the new appliance to be fitted and the installer has inspected the linerand is satisfied with its condition the liner can be reused. However, as the lifespan of the previous appliance and liner may not be known, it is strongly recommended the old flueliner is removed, the chimney swept, then a suitable new liner installed.

Use of flue liner on condensing appliances.

Wonderflex & Triplelock is not suitable for use on condensing appliances as the internal surface profile is convoluted and can hold aggressive residues caused by the flue gases which will attack and eventually corrode the stainless steel. Turboflex Plus can be used on condensing appliances, which have pressure at the flue outlet of 100Pa maximum, and provided the liner is insulated so condensation formation is minimised. It is also necessary to fit a tee and drain point at the base of the vertical system, adequately supported, and connected to a drainpipe to a suitable drain point.

Termination methods

Termination methods recommended by BS7566 Part 4

For gas burning installations, a flue terminal is required that complies with section 5 of BS715:1993. Where a proprietary terminal is not used, the free area of outlet openings on the termination shall be at least twice the cross sectional area of the flue. Outlet openings shall be such that they will admit a ball of 6mm diameter but not of 16mm diameter. The openings shall be uniformly distributed around the terminal or arranged at two opposite faces. (BS5440 Part 1). An approved terminal should be used to protect the end of the flue. A gas flue terminal must be fitted to an all gas installations of 170mm diameter or less.

For oil burning installations, a rain cap or universal terminal may be used, however, as there is a corrosion risk on such systems, regular inspection is recommended.

Multi-fuel Applications, Rain caps and universal terminals are not recommended for use on solid fuels, as the use of covered terminals will increase flow resistance and encourage the formation of aggressive condensates and deposits. In some instances, a terminal incorporating a spark guard may be demanded to reduce the risk of fire hazard. For all multifuel systems, regular cleaning is essential to prevent the accumulation of material which could ignite and create a fire hazard.