On 20/08/2019 14:07, Roger Hayter wrote:
On the subject of noisy fans, if you're thinking of using one the fans
with a counter current heat exchanger[1] with outside air (the Ventaxia
model at least) go for the six inch one, rather than the four inch one.
It is significantly quieter.

I took out the 4 " and replaced with a 6" and the idea was to replace
the 4" piping with 6" only to find out that where it went in to the
loft I had about 2 feet headroom and would have been eating insulation,
as for where it exits I dont know. So I got a 4" to 6" pipe adaptor and
used that.
Even in my younger days I would have struggled with the access.