I inspected a house with an unlined chimney with two separate flues. Each flue had a cleanout door. The water heater vented into the left flue and was backdrafting badly. The vent connector rise was less than 6 inches as required by the manufactures installation manual. Whirlpool manual says "CAUTION VENT CONNECTORS MAY NOT TERMINATE WITHIN A CHIMNEY
FLUE SERVING A FIREPLACE UNLESS THE FLUE OPENING IS PERMANENTLY SEALED." Does this mean the cleanout door must be sealed as well as the chimney opening where the vent connector enters? By the way, the cleanout door can't be sealed right now anyway. It is propped open by a gas line tapped from the water heater going up to a gas log. There were other problems as well.