removing multiple bricks for vent ?

[scrod]

Whilst investigating a suspiciously soft floorboard I was surprised to find myself plummeting through into a previously unexpected void space. Having crawled out of the hole and finished questioning the ancestry of whoever fitted it I then realised that the entire space was full of rot, probably wet rot but frankly there's so many layers of funghi down there the BBC would have a field day.
So I've bitten the bullet and ripped up all the floorboards and joists and bought new to replace them. I cant see any pipework or signs of leaks from outside so I reckon its the lack of air circulation that's causing the damp problem. There's only two air bricks fitted in the outside wall, both of which feed directly onto where the joists were sat, so with the cavity wall insulation as well I reckon it must have been blocked for years. I cant fit a direct link to the void space because of the joists so I was going to fit an s shaped telescopic vent (like this http://www.screwfix.com/p/telescopic-un ... vent/12025). Only now I can see the problem I reckon I'd have to cut out a square at least three courses in height to fit it from the inside. The wall doesn't look amazingly strong and already has some bricks missing where I guess someone's made an attempt to increase the airflow, so I'm worried that if I take out that many bricks at once it'll affect the integrity. Or fall down to call a spade a sodding shovel.
Has anyone else fitted one of these and how many courses of bricks is it possible to remove from the middle of a wall before being eligible for a Darwin award ?

Cheers for any advice
Scrod

[welsh brickie]

If your conserned, Install a concrete lintol in the wall before cutting out the brickwork.If you want to prop the wall above as your fitting the lintol,you can hire a acro prop and a plate that slides into the mortar joint called a strong-boy.