The concentric extension kit is used to extend the flue tubes as required, it is of the same diameters as the concentric flue kits. It can be supplied in various options, some of which are: male or female ends, (with ‘O’ rings on the 60mm diameter), and with flange for vertical application directly off the boiler and with test points for flue gas analysis. A centring spring is located between the two pipes. All versions are available painted or unpainted.