In an earlier contribution to this discussion,
Matthew J.E. Durkin wrote:

On a related note, how would I make the large vent holes in my
outside wall? Obviously I'm not going to be able to drill it. A cold
chisel will take me quite some time through the outside wall!!
I've seen plenty of suitable fittings, but am not sure how to make
the hole!

What size does it need to be?

You can hire core drills - along with a Kango hammer - for making clean
holes through masonry, but this may be an overkill for one hole.

The alternative is to drill a ring of small (typically 8mm) holes, and then
join them up with a cold chisel. In a cavity wall, I usually drill one -
maybe 1/2" - hole right through on the centre-line of the desired larger
hole. I then mark out a circle of the required diameter, concentric with the
pilot hole, on both sides of the wall, and then drill a ring of holes from
each side through to the cavity.

Whilst you *can* do all of this with an ordinary hammer drill, an SDS drill
makes it a hell of a lot easier.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.