In message , Harry Bloomfield
writes
Chris Green explained on 13/03/2021 :
We have an extract whose outlet faces downwards through the soffits,

The only none electrical ones I have seen, all rely upon being vertical
in a wall and need gravity to close them/ air flow to open them.

There are *spring close* versions but the springing must be very light
and I think they are limited to horizontal fitting.

We both need the *wax stat* version:-)

--
Tim Lamb