A zone barrel is what connects various ducting to the indoor unit. Moden zone barrels, such as the ones Ford & Doonan use, are proportional. This means they can be open and closed at 5% increments, meaning perfect airflow to all rooms.
Indoor Unit
The indoor unit is located in the roof space. It provides conditioned air into the home. The indoor unit is comprised of heat exchanger coils, filters, remote signal receiver and a fan. Ford & Doonan suspend the indoor unit over a drip tray, so that in the rare instance where a water leak may occur, the drip tray will capture the water before it damages the ceiling or insulation.