Re: Why line chimney?
With PVC flue you have a high efficiency boiler. The flue gas is low temp compared to the old system this does not supply enough heat to get proper draft for a large chimney. If you didn't have the liner installed the flue gases would never make it out the top before they cooled and dropped back down the chimney. With the proper sized flue the exhaust will exit the top with enough heat to rise and be carried away. The condensate should cause you no problems.
Be sure you live your life, because you are a long time dead.-Scottish Proverb