Quote:
	
	
		| 
					Originally Posted by Ducay  But if you've still got a traditional water heater, wouldn't you still need your existing stack and combustion air intake? | 
	
 
You do still need the existing b vent flue (assuming your hwt is not a high efficient one).  However, without a furnace venting into the flu as well, the flu will be oversized.  A chimney liner in tge existing flu is required.  As for combustion air, if your hwt is less rhan 50,000 btu no combustion air is required.  Hope that helps.