I have a zero clearance fp that I would like to install a free standing ps in. I see a 6 inch flue. Would it be best to use a 3 or 4 inch flexible liner to go from exit of chimney down to a tee-piece connection at back of stove or can I just place a horizontal pellet stove chimney pipe going straight thru fp back wall to the outside? I know this would create an unusable fp but we really aren't using it much. The ps would be sitting outside the fireplace on a non combustible pad. Ideas?