Basically your wall thickness should be 225mm, if its less fireboard it and tile the fire board so that it doesn?t look nasty
. So you do not need the fireboard if your walls are 225mm. Remember to keep 100mm all around the stove and the material behind is not combustible. The further back you put the stove the less heat will come into the room, which sometimes is more desirable. The more forward it is, then the warmer it is. To the ceiling you can use combustible material providing it is 450mm above the stove ie a wooden sleeper. I sealed my ceil then with stainless steel two battens and plaster board. Then when I get some fire board from site I'm going to add that. But as my ceiling is high in the fireplace its no problem. The measurements regarding stoves are massively over spec too. You could hold tissue paper 100mm from a stove and you will not get it to ignite. At worst the flue could ignite my plasterboard paper, hence fire board is better Returning to insulation, remember you may wish to let the brickwork heat up. I do as this takes ages to lose all its heat after the fire is out. It acts like a heatsink and provides heat back into the room after the fire is out. A good example of this is a cold morning but warm day so you light it early and then let the fire go out, but the fire opening stays toasty
Mind you I got good underfloor insulation, walls and loft and it does make a big difference Regarding a flue liner chances are you need one. Is the chimney internal ie is it on an external wall or a party wall on a semi detached. What size are the pot liners? If they are 225 or bigger then I?d put a liner in and fill the outer void with mica fill. Liner will cost you ?30 per meter, and mica ?7 a sack you?ll need 3 sacks. Easy as hell to put in your set up. But you could run it for a year and see how it goes then put a liner in if you got lots of build up in the chimney.
Basically you need to keep the gasses as hot as possible going up and out of the flue, so the wider the opening the colder the gas will get, it will slow and condense more and build up on the liners. But don?t panic about it, like I said you could try one season first. I just like to do things all in one hit so I don?t have to go back to it later.
My chimney is internal on a shared semi 225mm wall. Built with class 1 engineering bricks and has a 240mm square run with a very slow small bend. In fact its perfect, but I still put a 170mm (very tight) flue in and mica fill. So its something to think about. If in doubt up some piccies and we?ll look at it
