i need to get my gas furnace flew pipe out of the middle of my dining room. Can i elbow it over in the basement, come up against the wall upstairs, then elbow back over to the original place it was in the attic, then out through the roof?
NOT a good idea. Furnace venting is supposed to run straight and horizontal with a 1 inch per 10 feet slope upwards and a MINIMUM of elbows. You can get pressure switch tripping problems or fumes spilling out the front of the furnace if it is not done right.