Floor duct system, consisting of - a U-shaped duct lower part with side walls, a bottom and lateral cover holding profiles which are arranged in the interior of the duct lower part, - a removable cover which covers the interior of the duct lower part partially or completely, and is supported and held fixedly at least by the cover holding profiles, - at least one system carrier rail which is fastened releasably to the bottom of the duct lower part and serves to fasten electric installation devices and possibly as reinforcing webs or supports, the flow duct system comprising, furthermore, a lining abutting edge for each side wall, which lining abutting edge is configured substantially as a rectangular, strip-shaped, rigid bar which can be pulled out upwards, in order that its projecting vertical height can be adjusted and is constant along the entire bar, characterized in that, on each inner side of the duct lower part, in each case one lining abutting edge bears against spring clips which are cut out in the side walls, each side wall being connected to the cover holding profile by way of at least one horizontal web (9, 9'), in order to form a type of U-shaped chamber which is open towards the top and in which the lining abutting edge can be moved upwards and downwards, the lining abutting edge being configured as an L-shaped bar, the short limb of which has a thread at each end, through which thread a vertical screw is guided which is supported on the at least one horizontal web (9, 9') and which can be screwed from the outside, in order to move the lining abutting edge upwards and downwards, the bar being clamped between the spring clips and a contact face of the inner cover holding profiles, and the cover holding profile having, at its upper end, an edge which projects in the direction of the side wall and in which openings are in each case provided which allow the screw to be actuated from above in order to displace the bar and therefore the lining abutting edge upwards or downwards, or the cover holding profile being connected to the lining abutting edge, the lining abutting edge having a vertical adjusting screw at each longitudinal-side end, which vertical adjusting screw makes it possible, by way of being rotated, for the said two elements to be displaced upwards or downwards at the same time, the bar of the lining abutting edge having, furthermore, slots at each longitudinal-side end, which slots cooperate with corresponding horizontal tightening screws on the side wall, in order to lock the desired set height of the lining abutting edge and bar temporarily or definitively, and the bar being clamped between the spring clips and the tightening screws. - a U-shaped duct lower part with side walls, a bottom and lateral cover holding profiles which are arranged in the interior of the duct lower part, - a removable cover which covers the interior of the duct lower part partially or completely, and is supported and held fixedly at least by the cover holding profiles, - at least one system carrier rail which is fastened releasably to the bottom of the duct lower part and serves to fasten electric installation devices and possibly as reinforcing webs or supports,