klkbloke wrote:

1) I've seen a fan which operates on a humidistat, not connected to the
light switch in anyway. Has anyone had experience of these? Are they
any good. I'm looking at one for ~£30 from Screwfix.

Yup, I have fitted a couple of the 4" ones. They seem to do what it says
on the tin. You get in the shower - after a few mins the fan kicks in.
It then runs for 30mins to an hour after until the room is dry again.
You can tweek the sensitivity with a knob on the underside (you may need
to do this from time to time if the weather changes dramatically)

2) I have an airbrick - well it's actually cast iron. I was planning to
knock that through and use that to install the fan. The question is, do
I need to install a duct through the wall and a vent on the exterior
wall? Or can I just install the fan on the interior wall only? I would
prefer not to touch the outside of the house as the cast iron "brick"
is quite ornate (and 80+ years old) and fits in with the rest of the
house. Would I risk damp getting into the cavity? I'd assume I would be
no better or worse than the current arrangement?

As you suggest, if you don't line it then you will fill the cavity with
water. You can get rectangular ducting (TLC stock it), and a short
length ought to do it if you make sure it is sealed to the wall on the
inside and goes through as far as the cast iron on the far side.

--
Cheers,

John.

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