TRUMA BLOWN AIR HEATING DUCTING AND FITTINGS. The industry standard ducting and fittings used on most installations. The Truma blown air fittings will inter change with the older Carver system in all cases. The range of fittings allows simple installation of extensions to existing systems or the addition of a new system with a Truma TEB2 fan and a range of duct and fittings. The new design fittings are all grey behind the furniture apart from air outlets where there is a choice of colour.