I think these extractor fans are not a good solution anyway. Theyre
not particularly effective, theyre noisy and annoying, and the
bearings are guaranteed to deteriorate making them very noisy. And
they simply throw your heat away.
HRV, which costs very little more, works like a fan but recovers most
of the heat.
A window lock enabling it to be locked 1/4" open - good, effective and
free for most of the year, but not so good for the coldest few months.
Dehumidifier - a bit more to install, much more efficient, doesnt
ventilate or lose any heat.
Finally the simplest option of all, an adjustable vent. Easy, cheap,
simple, no run cost, and effective year round.
Anything but a fan, they are just the worst option.