Thank you for your question.
The chimney has been used to vent a coke back boiler, we would recommend you get the chimney swept and ask the sweep to do a smoke and draught test to assess the state of the chimney.
Show the sweep the chimney requirements in the user / installation manual, available on the product page download tab. He will be best able to tell you what the chimney needs.
The basics are:
Must be at least 125mm diameter minimum.
Minimum draught 12 Pa
Capable of withstanding heat of 220°C and above
No other appliance using chimney
No bends over 45 degree angle.
You can find a reputable sweep here - https://nacs.org.uk/sweep-search/
Hope this helps?