Increasing Adapter From Twin Wall Flue Pipe to Twin Wall Flue Pipe. Shieldmaster twin wall flue is CE approved for use in the UK, designation number EN:1856-1 T450 N1 D Vm L50050 G60. Crafted with ease of use in mind, Shieldmaster utilises a secure push fit connection which when connected with the provided locking band, creates a sealed joint between all parts.