If you look closely, you can see Dana standing atop the chimney.  At this job in Belmont he had to remove the existing liner (it wasn't the correct material for the appliance venting into it) & had to install the correct liner for the appliance.  I don't want to know how he got up there... to see another liner job http://www.dmstorrschimney.com/our-soot-stories/liner-custom-copper-raincaps-in-boston