making an opening to inset an electric fire

[PaulD]

Hope someone can help!

I want to put in an inset electric fire where there was previously no opening. The wall is an outside wall of breeze block construction. I probably only need to inset it about 65mm once I've brought the fire forward into line with the mantel and put the back board behind it - so not a deep hole at all. However, should I still be looking to insert a lintel to support this wall above the opening - despite the fact I am not knocking right through?

Afterwards I want to fill the gap between the back board and wall with fire cement and expandable fire proof foam - even though its an electric fire, not gas. Am I being over cautious?

Many thanks to anyone who can advise.

P.