@ ski & matthewjb. what was there before the stove? existing fireplace?
My home is a 1990 timber frame build, it had a standard external chimney with a square clay gas flue fitted inside, plus a tacky fake marble fireplace in front that you got with new builds at the time.
Took out the old fireplace, knocked out the existing fire brick back, amazed how much extra space you can get to your fireplace once that and the sand behind have been taken out, put in two lintels to support the existing flue, then a new liner and custom fabricated top plate, which also acts as a deflector for the Oak beam.