inline fan with 15m to 20m duct length and a bend

[Mmark]

I have an existing VentAxia ACM100 in one bathroom and I think it's brilliant.

I'd really like to run another inline from my other bathroom, as the "silent" one in the wall is noisey and poor extraction compared to my inline, but the distance is much longer. Depending which way the builders take it, it may be between 15M and 20M with potentialy one large bend.

I read the VentAxia's can only handle around 8M. Anyone have any other suggestions? Maybe another silent fan that can handle those distances?

Is there an easy way to calculate the rough ducting distance of an inline fan?

 

[Mmark]

The other option, is I have a much closer by flat roof (no eves space), that is directly above (after going past one floor). If I could put the extractor fan externally on that flat roof, that would be an option.