I have been doing a fair amount of work on a friends condominium. One rather annoying aspect of the place is that the range hood does not vent externally. I did replace the range hood with a modern grease and charcoal filter equipped model, but as cooking folks the heat and odors and moisture is proving too much. It would not be possible to vent the hood conventionally because opposite the wall behind it is another unit and the area directly above is living space. However, it would be possible to meander ductwork horizontally through some cabinetry and a wall and join it with the hot water heater exhaust stack, approximately 11' away. The exhaust stack is approximately 3" in diameter and clear and straight with some type of vent cap. The joint would of course be such that both ducts enter in an upward orientation (direction of flow). The duct from the water heater would be totally vertical in travel. The fan driven duct from the range hood would have to make some up and down moves and the range hood has a damper flap and is below the level where the two ducts would join. I have been told by folks at home supply/hardware stores that this is an okay plan. I have even been told that it is not against residential building code (LA City). However, I am most interested in whether or not it is a sensible idea and would appreciate any comments/suggestions by any knowlegeable folks here. Edited: Corrected water heater exhaust stack diameter to 3"