Hi there. I currently have a cast iron two brick height, what I call, air brick in the gable end wall just above ground level. It has corroded over the years and now I have a gaping hole there with just the surround in place. Are they called air bricks? as when I shop for them, I end up getting them vents for extraction etc. Is it better to go for a brick composition one, as I'm sure the cast is going to be expensive.