In message , ARWadsworth
writes

We were arranging a simple bathroom extractor (timed on exit if possible)
and realised the added expense of part P. One step further to a heat
recovery, low voltage extractor. But are there any *gotchers*?

Because large parts of the old ducting system are still there, a
centralised system might be possible but issues such as noise, cost of
running a dehumidifier, disposal of condensate, pressure balancing etc.
are a bit mind numbing.

I think we should pursue the cavity insulation aspect despite British Gas.
I believe the building is based on a concrete frame so the cavities might
be stopped at each floor.

My parents own the middle floor of a 3 flats. They managed to get cavity
wall insulation done recently. It just needs the people above and below to
have theirs done at the same time. Not everyone paid the same price as my
parents did not qualify for a full discount as it is not their place of
residence. I believe that they paid £150.

A humidistat fan in the bathroom may be better than a timed fan. And what
silly prices have you been quoted for a fan installing?

Huh! Still waiting.

Although the gas main (plastic up to the meter box) has been bonded,
incoming water supply and bathroom piping/metalwork have not.

We discussed fitting an in line ducted extractor with the estimator but,
as has been pointed out, any humidistat would have to be in the bathroom
itself and back to part P.

Whatever is done has to be tenant proof.

regards
--
Tim Lamb