timmmay:

 

Interesting, why did you put in a ducted unit with a single duct? Your design would be quite different from any other ducted unit, you don't need returns.

 

We could put a return under the floor easily enough, but then we'd need to run a 200mm duct from under the floor up to the ceiling cavity where the ducted unit lives. That's a pretty big pipe. I'd just put the return directly into the ceiling if I went that way.

 

I'm fairly confident that I'm going to order the Tamarak wall return grills from the US and install them low down, so the conditioned air is drawn across the room.

 

We have 4 outlets - lounge, family room, kitchen, hallway  and 2 returns, a small one in the ceiling (away from outlets) and a larger one at floor level in the other end of the hallway.

To get the duct from floor level back up to the ceiling we utilized the wasted space in a walk-in wardrobe where two wall units meet at right-angles.