We offer ducting kits in 2 different sizes, a smaller and larger size. The smaller size is often refered to as 5" however this is round ducting, the rectangular area equivalent is 150mm x 70mm. Anything less than this is classed as smaller than 5". We always recommend using the larger 6" Round or the 180mm x 95mm equivalent where possible as this will not restric the air flow and give the best extraction rates possible.