The maximum horizontal & vertical equivalent flue lengths (after the boiler turret and first elbow) is:
13m for iC Economiser Plus 27, iC24/28, iS 12/15/18/24 & iR 12/15/18/24 models
6m for iC Economiser Plus 35/39, iC36/40, iS 32/40 & iR 32/40 models
Allow 1.6 meters of flue length for each 87° bend
1.0 meters of flue length for each 45° bend.