Ducted air conditioning hides the machine and shows only grilles, which is why people want it and why it is the hardest system to retrofit. The indoor unit sits in a void, ductwork runs from it to each room, and the whole arrangement needs space, access and a plan made before the ceilings go up. Retrofitting into a finished house is possible and is rarely tidy.
What the building has to provide for a ducted air conditioning system
A void deep enough for the indoor unit and its plenum, usually a loft, a service floor or a purpose built bulkhead. A route for the ducts to every grille without crushing them round corners. A drain from the unit with a fall or a pump. An access hatch large enough to change a filter and to remove the unit one day. Miss any of those and the system is either not installable or not serviceable.
Where the air conditioning ducting goes
In a house with a loft, the unit sits above the ceiling and drops through into each room. In a flat or a single storey with no loft, ducts run in a dropped bulkhead in a hallway, which costs ceiling height and joinery. In a new build or a deep refurbishment the ducts go in with the first fix and nobody ever sees them, which is where the system is at its best.
Why ducted air con costs more
You are buying a refrigeration system and a ventilation installation and a builder's involvement. The unit, the ducts and the grilles are only part of it; the rest is forming the void, boxing the runs, making good, and the extra survey work needed to establish that the route exists at all. It is also a longer job with more trades on site.
Zoning is the point of it
A well designed ducted system is zoned, so bedrooms and living space can be conditioned at different times and temperatures. Without zoning you are conditioning the whole house whenever anybody wants one room cooled, which undoes much of the running cost advantage. Ask how many zones are in the quote, because the answer is often one.
Questions people ask about ducted air conditioning
Can ducted air conditioning be retrofitted?
Into a house with a generous loft and a sensible plan, often yes. Into a flat with a concrete soffit and no void, usually not without losing ceiling height to bulkheads. The survey answers it, and the answer is about the building rather than about the equipment.
How much loft space does it need?
Enough depth for the unit itself with service clearance, plus room to run ducts at their proper diameter rather than squashed. Squashed duct is the commonest cause of a ducted system that is noisy and underperforming, because the fan has to work harder for less air.
Is a ducted AC unit quieter than a wall unit?
In the room, yes, because the machine is not in the room. The noise moves into the void and into the duct, which is why duct sizing, flexible connections and grille selection matter. A cheap ducted installation can be noisier than a good wall mounted one.
Does ductwork need insulating?
Yes. Duct carrying cool air through a hot loft will gain heat and sweat, so the runs are insulated and vapour sealed. Uninsulated duct in a loft is both an efficiency problem and a condensation problem, and the condensation is the one that damages ceilings.