On 23 Feb 2021 at 16:45:04 GMT, "Polskasweetie"
wrote:

Sorry, forgot to mention it is for a 2nd floor (of a 3 floor) flat so unsure
how long or short the ducting is, or where it actually goes out to.

It is probably best to assume a moderate length of duct then, because you need
a fan suitable for a duct as the common, cheaper ones will not work very well
at all with any significant length of duct (more than 400mm or so). The exact
length of duct will affect efficiency but if you don't know the length then it
it is reasonable to get one designed for ducted use so it will work even if
you don't know exactly how well.



--
Roger Hayter