Extending fire opening for log burner

[Gareth6789]

So I'm looking to extend my fireplace opening to fit a log burner. I can get a small size burner at the moment but I would like more space around it as I think it looks much nicer. I have capped the old gas system and opened it to the original fire opening which is made of concrete blocks and a lintel block, which appears to be holding up a 9" clay liner. This is where my problem is. I don't know whether or not the clay liner will fall through, or if the wall will be stable enough to hold its self whilst I change the lintel to a larger lintel, higher up. Would I have to remove the liner first? Or is it self supporting? Is the job easy enough to do, or is it better to just leave it as the smaller opening?

 

[theprinceofdarkness]

It looks as though the back of the tapered section is sitting on the edge of a block. I would cut two legs out off 2" X 2" or bigger and fit them in under the front side of the tapered section and fit them with thin tapered wedges.
I would cut the hole as big as possible because it looks better, it lets you use a bigger fire - small fire only take small logs - do you enjoy cutting up wood? and it lets more hot air out from the back and top of the fire into the room.
Another problem a transition flue between your fire and the existing flue. Another potential problem is the flue material, I can't remember which is which, but a different grade of flue is required between fuels. I used the multi fuel type (type 2) its about three times the cost of the type 1.
Frank

 

[Gareth6789]

Right, yeah I will more than likely use a stainless steel liner inside the current liner, the problem is that I don't know if the flue liner will fall out if I remove the lintel, as I would like to lift the current lintel higher and put a wider one in to be able to support a wider opening

 

[theprinceofdarkness]

I can't see from the pic. what the flue is made from. I would guess its a load of shortish concrete pipe, say 35 cms long*. As the build goes on extra pipes are mortared in on top of yesterdays work. All of these are sitting on that bottom section. If its a really good job, the gap between the brick flue and the liner will be filled with vermiculite. This would make it extremely problematic to do what you are intending. Removing a bottom section could results in all or some of it falling down on your pinkies.
As a start I would find out what the material is and Google for " concrete chimney liner" or what ever. When you can find a manufacturer, go to their site and see what the installation instructions are.
Frank
* slide a stickup the flue to see how long each section is by the roughness at the joints.

 

[stuart45]

Right, yeah I will more than likely use a stainless steel liner inside the current liner, the problem is that I don't know if the flue liner will fall out if I remove the lintel, as I would like to lift the current lintel higher and put a wider one in to be able to support a wider opening

The fireplace lintel and integral throat will be holding up the liners, although if the vermiculite has been stabalised with cement it will help hold the liners in place.
You can get a long drill bit and go through the bottom liner and leave it in place until you get a raft lintel etc in.

 

[theprinceofdarkness]

So you stand the flue on legs, do the lintel work (beware of a cubic metre of vermiculite on your floor!). Then Stuart 45's answer suggested to me that if you drilled a hole just above the lintel, say about 1/2" diam right through the flue liner and into the rear wall of the chimney breast. Then if you slid in a 1/2 steel rod it might be able to support the whole flue length (5 cwt?). Tapping gently one of the leg wedges would tell you whats happening.
If it seems secure then the bottom bit could be removed, but this is the problem, to be able to refit the bottom bit at exactly the correct height, bearing in mind where the original tube joints are. If it was wobbley, then another leg holding the centre of the rod up might help things. If you end up with the flue at the correct height and being supported then you could cement in two pieces of angle iron into the back wall and through the front wall (less 1") which are right under the edge of the liner, thus supporting it. The bar could then be withdrawn when the angle iron mortar has cured. I can't think of a way to trim the height of the flue in-situ.
Frank