The heater had to go. I drilled out the rivets, pulled the unit out through the outside wall and removed the flakeboard shelf that supported the unit. PO had added a pressure tank in the water line. I took that outa also. There had been leaks
from an unknown source so I took out the water tank and dismounted the water pump. I'm about to redo all connections, vacuum out all of the moldy crud, wash everything with a bleach solution and paint
the floor after it's thoroughly dried. I''ll fasten a painted wood panel on the inside of the opening and use the old outside vented cover to fill the opening. Oh and carefully cap the gas line too.