I used to fit wood burning stoves for a living. The single wall chimney system that’s installed and you plan on using are fitted and fine tuned to each stove. They need positive pressure to ensure that the carbon monoxide is drawn out. Any kind of alteration to it you asking for serious trouble if you don’t know what you are doing. Carbon monoxide has no smell and it will kill you VERY quickly.
Please find an alternative way to extract 
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