How to fill in disused Fireplace (Ed.)

[wdaus]

Hi,

Can anyone help with how to fill in this hole?

It used to be a gas fireplace but it's been removed. The flue has been taken down below roofline and tiled over.

What's the best way we can fill and plaster so it's flush with the rest of the wall?

And do we need an air vent seeing as the flue is below roofline?

It's about 40cm high , 26cm wide.

Thanks in advance!

 

[Wayners]

Bricks or blocks with sand and cement. Brick it up slightly back a bit to allow for plaster thickness.
Few long screws either side that line up with the new mortar joints. Probably one each side will be enough somewhere around the centre.
Vent is required if you have open chimney. Let the air through and stops condensation.
If it's blocked offs at top then don't bother with a vent.
PVA.
Multi finish plaster.