This is a picture looking down into the chimney as it is being rebuilt.  This is a six flue chimney, being rebuilt using wythe bricks to divide the individual flues.  The pipes seen in the upper left flue are the vents for a high efficiency gas boiler.  Two vents are necessary, one is to vent the combustion from the appliance and the other is for intake air.  For earlier photos of this project http://www.dmstorrschimney.com/our-soot-stories/pinckney-st-beacon-hill-rebuild-con-t-