I'm remoldeling a kitchen, and in a section there is a chase with clothes chute and 6" flue pipe. Chute will be removed, but, have to do something with flue pipe. Furnace was upgraded to energy eff. furnace, so it no longer uses 6" pipe. 3" water htr. Flue is still tied into it. Can I put a double wall vent pipe/b vent inside the common wall between kit. And family room? If not how close can I put the pipe in the chase to surrounding walls as to make chase as small as possible. Thank you in advance for any help in this matter. Denman