Ducted air conditioning in a Spanish flat
It is the system that looks best in a renovated flat and the one that most constrains the project. It is decided before ceilings close, never after.
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Short answer
How a ducted installation is organised
In a ducted system an indoor unit hidden above a dropped ceiling pushes air through insulated ducts to grilles in each room and draws it back through a single return grille, with the outdoor unit on a light well, a roof terrace or the façade. With the machine over the hallway you lose 25 to 35 cm of height in that strip and 15 to 20 cm along the duct runs. The other two requirements are an authorised position for the outdoor unit — the point that kills most projects — and enough electrical power. It makes sense inside a full renovation, which in Barcelona runs €780–1,600 per m² over 10–14 weeks; in a finished flat it rarely does, because it means rebuilding ceilings you have just paid for.
There are five components, and the one that decides whether you are happy is not the machine. It is the return.
The parts of the system
- Indoor unit above a dropped ceiling, usually over the hallway or the bathroom
- Insulated ductwork to every room
- Supply grilles, one or two per room depending on area
- A return grille, the most underspecified part and the usual source of noise
- Outdoor unit with its own electrical supply and a condensate drain
The Spanish layer
What the building has to allow
Five checks come before any design work, and two of them are legal rather than technical.
| Requirement | What to check | Who decides |
|---|---|---|
| Clear ceiling height | 25–35 cm lost under the machine | Site visit |
| Outdoor unit position | Light well, roof or façade, in writing | The comunidad |
| Contracted power | Unit load added to the flat | Installer, via boletín |
| Condensate drain | Fall to a real drain, not a light well | Design stage |
| Maintenance hatch | Filter access without breaking the ceiling | Design stage |
The outdoor unit is the hard conversation
The façade, the light well and the roof are common elements: they belong to the building, not to your flat. Hanging a machine on any of them needs the agreement of the comunidad, the owners association every Spanish block has, and it is minuted at a meeting. If the building is listed, façade equipment is often simply prohibited. Write to the administrador — the managing agent — before you accept a quote, and keep the reply.
Power and the boletín
Older flats often still run on the contracted power set decades ago, and a ducted unit adds a meaningful load. Raising it means a new consumer unit and a boletín — the certificate a registered installer issues under their own number, which the supply company requires before changing your contract. Routine while the walls are open; disruption for nothing afterwards.
Design
Zoning, return air and noise
A badly designed ducted system conditions the hallway and abandons the bedrooms. Three decisions separate the two outcomes.
Zoning
With motorised dampers and a thermostat per zone, each room takes only what it needs. In a through-flat with bedrooms on the light well and the living room on the street, the orientations behave so differently that zoning stops being a luxury.
The return
This is the most common failure. An undersized return makes the unit fight for air, raises noise and drops output. It has to be properly sized, reachable so filters can be changed, and far enough from the supply grilles that the air does not short-circuit back.
Noise
A well-built system is close to inaudible. When you hear it, the cause is usually excessive air speed in undersized ducts, a small return, or no acoustic isolation under the machine’s mounting frame — decided on the drawing, and not fixable afterwards without opening the ceiling.
Mouldings and high ceilings
A period flat with three-metre ceilings swallows the machine easily, but the dropped ceiling should be an interior decision rather than a blanket one. Lowering only the hallway, and leaving the main rooms with their height and plaster mouldings intact, is what separates a good installation from a flat that has lost what made it worth buying.
Alternative and oversight
When splits win, and what to photograph
Ducts are not always the answer, and in some flats they are the worst available option.
Choose splits if
- There is not enough clear height for ducts and a dropped ceiling
- The ceilings have mouldings or coffering you do not want to lose
- Only one or two rooms actually need conditioning
- There is no full renovation and no ceilings will be opened
What you trade
With splits the machines are visible and the distribution is less even, but the installation is far simpler, cheaper and does not touch ceilings. Before sizing anything, insulate: new external windows and insulation in the shutter box cut demand, and then any system can be smaller. A large machine fitted to compensate for a leaky envelope pays twice for the same problem and cycles in short bursts, which is exactly when you hear it.
Running it from abroad
Ask for three dated photographs before the ceiling closes: the full duct run with its insulation, the return path with the filter access visible, and the condensate drain showing its fall. Ask where the maintenance hatch will be, and get that on the drawing. A ceiling closed without a hatch has to be broken open the first time the unit faults, and that fault always arrives in August.
Frequently asked
Common questions
25 to 35 cm in the strip holding the machine, usually over the hallway, plus 15 to 20 cm along the duct runs. In a period flat with three-metre ceilings that is no problem; in a 1970s flat with 2.50 m it needs studying first.
Yes. The façade, the light well and the roof are common elements belonging to the building, so the comunidad has to agree and it is minuted. In a listed building, façade equipment is often prohibited outright. Ask the administrador in writing before accepting a quote.
Often, because the unit adds real load to an installation sized decades ago. It means a new consumer unit and a boletín, the certificate a registered installer issues under their own number, which the supply company requires before changing your contract.
In a through-flat, yes. Bedrooms on the light well and a living room on the street behave completely differently, and without motorised dampers and a thermostat per zone you pay to condition empty rooms.
Splits. Ducts mean opening and rebuilding ceilings, so outside a full renovation you pay for the same ceiling twice. If the ceilings carry mouldings, the case for splits is stronger still.
Next step
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