Opening up a chimney recess

[aka123]

My chimney brest currently has a small gas fire in a fire back and I want to open it up to install a log burner. New opening would be 0.9m wide by 1m high. I have taken the plaster ceiling down (for another job) and now find that the chimney breast stops at ceiling height and resting on it is a 7" deep I beam which runs across the room and supports the floor joists for the room above. The beam is central above the fire opening and I can see the brick flue offset at ceiling height. The chimney breast (19" deep by about 4ft wide is also solid at the top so I assume that it is solid all the way through (apart from the flue of coarse). Has any one come across anything like this before and how would I support the weight above to create the opening (the house is about mid 60's).

Thanks

Steve

 

[noseall]

at only 900mm wide, a 75mm x 100mm p.c.c. builders lintel will suffice.

 

[aka123]

Thanks for the advise noseall, but the chimey breast which is 450mm deep seems to be solid and not a single run of bricks/blocks at the front. How does a 75mm x 100mm lintel support this ?