I have had 2 Carrier 48XP Electric Cool / Gas Heat 3 ton package systems installed as a retrofit on the flat roof of my one level home. The install splits the house into two zones ( A & B) of approx 1000 sqft each, i.e. a packge unit for each zone which connects to the existing independent metal boxed ducting which runs through the center of each zone with braches to each room served by the zone, there is no interconnecting ducting between the two zones, each zone also has its own humidifier and thermostat. The input ducting from the XP48 units connect to the existing ducting and are short runs approx 4ft long. The return ducting to the XP48 units is on the roof and are made from 24" x 14" metal which has 2" insualtion on the inside wall of the duct, these runs are approx 12ft long. Each return duct connects to its own 24" x 14" ceiling mounted return vent which have a 1" electronic Air Cleaner installed. I hope this explains the layout of the install.
My concern is the positioning of the return vents, the return for Zone A is next to the busy rear door of the house and the return vent for zone B is located within the conditioned space of Zone A, is this OK or what, thanks