Woodburners are very different to open fires , generaly they are 80% efficent compared to open fires which are 20%. The stoves due to their design burn the wood gas which helps to raise the efflux temperature to a much higher level than is achived with an open fire.
A chimney which works well for an open stove could be hopeless and possibly dangerous. If the chimney is cold/wide where the stove pipe ends the eflux will cool rapidly and cause much to build up. With a liner the stove will draw much better and will be easier to sweep.
The Hetas regs are easy to understand and straightforward in the main. A Hetas installer can sign off somestuff which the regs say should be done ie hearth size.
As for price we were quoted £990 to fit a liner and to DIY with a 904 liner (the more expensive)will cost £550 ish. Building control will sign you off for about a £100.
Google around and read whats about and between them all you can work out what to do.
Need to tell your house insurance and either get it signed off by building control or installed by Hetas other wise your insurance will be invallid.
Check your not in a smokeless zone to and suss out a supply of wood first and where you will be storeing it , you cant just burn any old wood. Well you can but you could have big problems with your chimney and possibly a fire.
Can you tell I have been mugging up on this 🙂