Is there limitations to the length of the outside air intake duct? I have a Harman P61-2 and would like to install the outaide air intake and it would have to be 15-20ft long as the stove sits in the center of the basment and vents into the chimney. I would go straight up and make one 90 then straight out above the drop ceiling and out the back side of the house. Was thinking of using 4" round duct.