Chimney breast woes help needed

[thewall]

I'm in the process of installing a stove and started to open the chimney breast then i found this lintel/slab which has the bricks of the brick flue sat on but i need to have the opening wider than the lintel/slab by 6" either side,i'm going to put in another lintel,but i'm worried that if i take out the old lintel/slab the bricks might move.The chimney breast is 56"x15",hope you can understand my pic

 

[theprinceofdarkness]

Normally flues are just a "box" with the sides being two bricks thick and the front being one brick thick. As you have found out there is a lintel across the front opening. Somewhere as in your case there is a register plate, which blanks off the huge hole with a hole in it for the flue liner.
So have you checked to make sure that your register plate is as thick as you have shown and its part of the chimney breast and is it embedded into the sides of the flue, carrying the weight of the bricks at the sides? If it is, as in your sketch then you have a problem as it will have to come out and then what supports the bricks sitting on its side?
Frank

 

[ree]

What dimensions do you need for the new opening - the width and the height?

The Mfr's Instructions with the new stove will give the dimensions needed.

When you say "stove" what exactly do you mean?

Chimney breasts are typically about 1500mm wide.

Why not post a pic of the chimney breast showing the lintel if possible?