If I stick by the stairs funky Dunc then there is hardly any space around diffuser (weird cupboard thing above stairs. So only one side would be clear. If I stick central then there are two long hallways with no restriction (manual states you need up to 1m clearance on fastest setting) I guess it would still work but as dudie mentions suggests downdraft would be an issue.
Also I would have to install under the ch / cw water tanks which would be a bit of a pain 
Just wired the unit up to a spur and seems that pretty quiet! Only annoying thing is that the fan blade was catching on the plastic case..... So popped filters off and centralised the fan. Should not really have the do that on a brand new unit! But it's all fine now. Pretty poorly made if I am honest.... Cheap plastic housing which does not fit together well. Will see how it goes tomorrow when I install.