Ducted AC - quick duct size calculator?

[Alan Ambrose]

While we've still got the roof open, I would like to put in some ducts for potential ducted AC into the bedrooms. Anyone seen a good duct size calculator? Or just some simple rules of thumb?

[Russell griffiths]

Do you mean a whole house ducted system with a main unit in the loft, or do you mean like a split system with a unit on the wall. 
my whole house ducted system used 200mm flexible insulated ducts if that’s what you mean, one to each bedroom and one each in the front room / lounge areas. 

[Alan Ambrose]

>>> Do you mean a whole house ducted system with a main unit in the loft

 

Yeah, that one. I'm leaning towards 180mm foam ducts atm, which sounds like it would work.

[Nickfromwales]

Chaps. 
 

AC or MVHR?