Take a Paws, page-31447

I thought you had reverse cycle aircon but you mentioned Brivis and they only do Evaporative cooling and gas heating, Rinnai who own Brivis do RC aircon.

Bit odd that upstairs gets like an oven, cold air does go to the lowest point but still

I have 5 zones, 3 bed rooms, lounge and kitchen/dinning, the latter two is open plan but I still operate each zone separately. This is my second summer with aircon and it has no problem maintaining 22 degrees even when it's over 49 degrees out doors