Hole in wall from ducting

Hi

I recently discovered a crator in our bedroom wall which was covered up with some plywood. It appears to have been created when the previous owner had the bathroom extractor fun ducted outside. Please see linked diagram and pics.

http://www.geocities.com/siculster/dscf0735.jpg
http://www.geocities.com/siculster/dscf0736.jpg
http://www.geocities.com/siculster/pipe-box.jpg

I got a handyman in last week to give me a price for filing in the hole and replastering the part of the wall. On inspecting the ducting he could see that it was about 3-4' short of the actual vent and said it wasn't a problem. However he wasn't keen on filling the hole in immediately around the piping as he felt there should be some ventilation getting through to the entire pipebox.

I'm not too sure if this is right. I'm keen to get the hole filled in for insulation purposes.

What does everyone else think?

I'd fill it in too. Rooms are drafty enough without extra holes there.

the ducting should be connected to the exterior grill to prevent venting into the cavity.
the brickwork can then be reinstated and plastered properly.