In message ,
(N. Thornton) wrote:

"Trevor Smith" wrote in message ...
I am fitting an 4" extractor fan in the bathroom wired from a junction box
on the lighting circuit so does it still need a double pole isolator
switch?.

If you have no external wall there you need one, but otherwise I
wouldnt bother. People often fit these in the hope it will clear
smells or damp, but really theyre fairly useless. A far more effective
alternative is a locking mechanism that allows the window to be locked
securely 1/2" open when wanted. 4" fans get noisy over time, waste
electricity, throw heat away, and are simply ineffective.


Have you had experience of humidistat control? If damp is the issue, it
should be the cure and I'm thinking of fitting one, but I completely
agree with your point about wasted heat.

As I see it there are three ways around the heat thing:

1: make sure the only air leaks into the bathroom are from the heated
part of the house - doesn't stop wasting heat (but then neither does
leaving the window open), but doesn't cool the bathroom too much;

2: use one of those rather expensive in-wall heat-exchanger things.
Looks like an ordinary 4" (or 6") from the inside and outside, but in
reality is an air exchange unit which uses the heat from the outgoing
air to pre-heat incoming air;

3: install one of those very expensive whole-house mechanical heat
recovery and ventilation systems, beloved of IMM.

Hwyl!

M.

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