Hi mate once again thanks for your patience,I aint to bright with numbers & calculations,been up and looked at my fans,nowt on them,looked for their manuals,god knows where they are..probally roached.

Checked where i got them from and from memory my 6" intake is a lti rvka1 and I think 6inch=125mil

On that it says 420 hahaha the gods are shinning! 420m3/per hour

My extractions are 2x5" so thats = to 2x100mil...I think?
and they both shift 275m3 per hour each x2= 550m3 per hour...or have i got this wrong lol..I do apoligise rather mullard this end,as always thx tho I appreciate your help.

Baldy.