The present invention provides a vent-pipe installation and support system for installing and supporting a vent-pipe system above a joist. This system comprises perpendicular vent-pipe supports for supporting vent-pipes which run generally perpendicular to the joists, and parallel-vent-pipe supports, for supporting vent-pipes which run generally parallel to the joists. The perpendicular-vent-pipe supports comprise a body portion, which is mounted to a joist, and a top portion having a generally C-shaped cut-out. The C-shaped cut-out opens away from the joist, and is sized to fit the vent-pipe, The body portion has graduated markings parallel to the joist top surface, wherein when consecutive graduated markings align with the joist top surface on every other consecutive joists, a supported vent pipe will be at a required grade. The parallel-vent-pipe supports comprise a post having a top, and having a mounting surface, whereby the post mounting surface is mounted to the joist, and a pipe engaging member extending away from the post mounting surface, wherein the pipe engaging member is at the top of the post, and wherein the pipe engaging member is a generally C-shaped cut-out. The C-shaped cut-out opens away from the joist, and is sized to fit the vent-pipe. The post has graduated markings parallel to the joist top surface, wherein when consecutive graduated markings align with the joist top surface on consecutive parallel-vent-pipe supports when the parallel-vent-pipe supports are spaced a predetermined distance apart, a supported parallel-vent-pipe will be at a required grade.