Install furnace venting by locating a place on the roof for the vent pipe and cutting out an opening, attaching the vent pipe and sealing the edges. This project requires a reciprocal saw, a vent pipe, vent flashing, a vent cap, roofing cement, roofing paper, a tape measure and shingles.
Purchase vent pipe and flashing according to the furnace manufacturer's recommendations. For instance, the manufacturer recommends either sheet metal or vinyl pipes. Locate a suitable location for the pipe, and draw a circle on the spot that is the diameter of the vent pipe. Use the reciprocal saw to cut the circle in the roof, and remove the immediately surrounding titles.
Run the vent pipe up through the roof, making sure that it extends at least 12 inches above the roof so that the gases vent instead of re-entering the house. Place a flashing collar around the base of the pipe where it rests on the roof. Attach a T-end fitting and a pointed cover at the top of the pipe. Place roofing cement and paper around the edges of the of the collar to seal the edges and prevent leaks. Finish by cutting and attaching new shingles to fit around the pipe.