On 6 Apr 2006 06:10:03 -0700, a particular chimpanzee named
randomly hit the keyboard and produced:

There are no trickle vents in the uPVC window in my bedroom. 2.5m wide
x about 1.2m high.

I am thinking of fitting one or two white plastic trickle vents. I
presume it is just a matter of drilling a few small holes through the
frame?

For the reasons already explained, perhaps not the best option.

Consider instead, some form of passive stack or mechanical whole-house
ventilation instead; http://www.passivent.com/ for example.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"