I'm planning to instal an oil fired non-condensing combi boiler(Grant) in
the kitchen of an old cottage.
There's an existing, but disused fireplace in the kitchen and the chimney
looks good.
Is it enough just to fit a length of 4in flexible liner onto the boiler and
route it up the chimney,
with the boiler taking its air from the kitchen?

I take it I can't use a balanced flue discharging into the fireplace!