Question: I would like to finish our basement and heat it with a (natural) gas firplace/stove. I have two questions. 1) Can a top-vent unit use an existing chimney that is currently being used by the furnace and water heater? 2) Can a direct-vent unit be placed on an interior wall (the room on the other side will be for storage in the unfinished portion of the basement) and have the vent pipe travel horizontally eight feet through the storage area? Answer: 1. This is not usually addressed in the manufacturers instructions that I have seen. I suppose that it might be ok provided that the BTU input of the 3 units together is within the capacity of the chimney. Your heating many has a chart to show this capacity. 2. Yes, certain Direct Vent units allow for horizontal travel up to 10 feet or more to the outside wall. Check the manual on any specific unit that you look at.