Centrotherm Innovent PP installation ?

Raggy

Regarding venting, has anyone deadheaded the computation air in the same chase as the venting. I have a tile lined cinder block chimney that was once used with a inefficient oil boiler and I worry about contaminated combustion air form existing black soot and particulate lining the chimney. Maybe I'm over thinking this but I remember this instructor at the TT training class stating fresh clean combustion air is a must or damage to equipment will result. What is you experience? I'm using 25ft of centrotherm polypropylene flex to run the vent gasses out the top of the chimney with a termination kit that allows combustion air to be pulled in from the top without having to run a separate 25' pipe for combustion air. Easier said, combustion air pipe is terminated in chimney just above the appliance.