Ceiling cassette aircon: what you own above the grille
Most people never chose the cassette in their ceiling. It came with the flat or the office, and everything except a grille sits out of sight. What is hidden up there decides how the unit behaves and what looking after it involves.
By Team Snowflake | Updated 5 Aug 2026
A box in the ceiling with one face showing
A cassette is a complete indoor unit fitted into the ceiling with only its face left visible. The body sits in the void above, out of sight and out of reach. What the room shows is a flat square or rectangular panel, level with the ceiling, carrying slots along its edges and a grille in the middle.
Air travels in two directions across that single face. Room air is drawn upward through the centre grille, and cooled air is pushed back out through the slots at the perimeter. Vanes in those slots set how far the outgoing air is thrown and how steeply it drops.
Panel size is the only clue most occupants get about what is behind it. In a commercial suspended ceiling the panel lines up with the tile grid, because the unit was chosen to drop into that grid. In a condo living room the panel sits in a plastered ceiling with an opening cut around it.
Nothing visible from the room names the make, the capacity or the age. That sits on a nameplate on the body above, readable only once the panel comes down.
The centre draws, the edges blow
That pattern is the whole design argument. Return air arrives from directly below rather than from one wall, so the unit never has to drag room air the length of the floor to reach its own intake.
It also makes the space beneath the panel part of the machine. Anything filling that space changes how the unit performs without anything being broken. Tall shelving, a partition run up to the ceiling line, a hanging display or stacked stock will all do it.
If a cassette went weak after a fit-out and nobody has looked at what now sits under and around the panel, ask for that first. It is quicker to check than a coil, and a fit-out is the most common thing to have changed.
Why the shape wins in an open room
A cassette spreads air more evenly across an open floor than a wall unit can. That is why it dominates offices, shops and larger condo living rooms.
A wall unit throws one stream. Mounted high on one wall, it pushes air in a single direction, so the far corners receive whatever is left of that stream once it arrives. In a bedroom that is more than enough. On a floor with desks along three walls it is not.
A cassette starts from the middle of the ceiling and pushes outward on every side it has. The distance to the furthest corner drops sharply, and the air reaches that corner with less of its travel already spent. Occupants feel this as fewer warm pockets rather than as colder air.
The shape is not free. It needs a ceiling deep enough to swallow a body, an opening cut into that ceiling, and a route out for pipes and water. A wall unit needs a wall and a hole through it. That difference decides most of what follows on this page.
| Room situation | What a wall unit does | What a cassette does |
|---|---|---|
| Room situationBedroom with one free wall | What a wall unit doesCovers it comfortably from a single direction | What a cassette doesMore ceiling work than the room asks for |
| Room situationSquare living room, no long free wall | What a wall unit doesBlows across from a corner, leaving cold and warm zones | What a cassette doesReaches all four sides from the middle |
| Room situationOpen office floor, desks around the edges | What a wall unit doesTakes several units to reach every side | What a cassette doesCovers the floor from fewer positions |
| Room situationDeep shop with a narrow front | What a wall unit doesThrows one way, so the rear stays warm | What a cassette doesSpreads from above, though the rear still runs warmer |
| Room situationFlat with a plastered ceiling and no void | What a wall unit doesFits on a bracket with a pipe route through the wall | What a cassette doesNeeds a bulkhead or false ceiling built before it can go in |
What sits above the ceiling
Most of a cassette is above the panel, and the hidden portion holds everything capable of going wrong quietly. A wall unit wears its problems in view. This one does not.
Seven things share the void. Each has its own behaviour, and only the first two are reachable without opening the ceiling.
- The casing, a metal box hanging from threaded rods anchored into the slab above.
- The filter, sitting immediately behind the centre grille where the return air enters.
- The coil, the cold fin surface that air crosses on its way through the casing.
- The blower, mounted centrally, pulling air up through the grille and flinging it outward to the slots.
- The drain tray, a shallow pan under the coil holding whatever condenses on it.
- The float switch, a level sensor in that tray which stops the unit when water rises past a set point.
- The pump, lifting collected water up and out of the tray so it can leave the building.
Why a cassette needs a pump at all
Water leaves a wall unit by falling. The outlet sits at the back of the casing, the pipe runs down inside or along the wall, and gravity does the whole job unassisted.
A cassette has nowhere to fall to. Its tray already sits at ceiling level, and the water has to cross the void to reach a stack, a gully or an outside wall. A pipe sloped downward for that entire distance would drop below the ceiling line long before it arrived.
A condensate pump solves that by lifting instead. It raises the water a short way to a high point in the void, and from there the pipe falls the rest of the distance. The lift is what buys the run its drain gradient.
This is the defining ownership difference. A cassette has a moving part in its drainage that a wall unit does not, and that part needs power, a clear impeller chamber and a float that can move freely. A condensate pump fault behaves nothing like a blocked pipe, and it has its own guide.
What the pump changes about a leak
A pumped unit usually announces a drainage problem by stopping, not by dripping. The float rises as the tray fills faster than the pump clears it, and the switch cuts the unit before water reaches the panel edge.
From the room that reads as an aircon which switched itself off, or as a code on the wall controller. It does not read as a water problem at all, which is why the tray is so often the last thing anyone looks at.
Visible water is the later stage or a separate fault. By the time a ceiling stains, water has been going somewhere it should not for a while, and the ceiling itself is now part of the repair.
If a cassette keeps shutting itself down and the first quote names the control board, ask whether the tray, the float and the pump were checked first. Water in a tray is the more common cause and the cheaper one to rule out. Which fault pattern applies is a separate question, and the cassette fault guide separates them.
Access is what makes upkeep different
Every job on a cassette begins with getting to it, and that single constraint shapes how the work is scoped, scheduled and charged. Nothing about the machine is harder than a wall unit. Reaching it is.
The panel drops on clips or screws, exposing the filter and the underside of the casing. Light work stops there. Anything deeper needs the void itself opened, which in a suspended ceiling means lifting tiles, and in a plastered ceiling means an access hatch, assuming one was left.
A missing hatch is the most common ownership regret on this format. A ceiling gets closed up during renovation with no opening left near the unit. The next person needing to reach a pump, a joint or a wiring point has to cut plasterboard and make good afterwards. If a false ceiling is being built around a cassette, that is the moment to decide where the hatch goes.
The floor below matters too. Sheeting has to go under the unit before anything is opened, because everything coming off the coil and out of the tray lands directly beneath. In a shop, a clinic or a working office that means clearing the area and often working outside trading hours. Servicing a cassette is treated as its own job for these reasons, and the cassette servicing page sets out what it covers.
The void is shared with everything else
A commercial ceiling void is crowded. Sprinkler pipes, cable trays, lighting drops, structural beams and other building services run through the same space the cassette occupies, and they were not laid out around it.
That crowding shows up twice. It limits how the drain and refrigerant runs could be routed at installation, which is where an awkward pipe route usually comes from. It also limits how the unit can be reached later, because a technician has to work around whatever was installed after the aircon went in.
A beam is the version worth knowing about. A drain line forced to cross under a beam loses height it cannot recover, and the run past that point has to be pumped or re-planned. Where a ceiling drip has a long history and no clear cause, the route above is worth mapping before anything else is replaced.
Variants: one-way to four-way, compact to full-size
Cassettes are described two ways: how many sides they blow from, and how large the body is. Both are fixed at installation.
Four-way blow is the default and covers most of what gets installed here. Two-way suits long narrow rooms and corridors, where blowing into the two near walls would waste half the output. One-way behaves like a wall unit mounted in the ceiling, and turns up in small rooms and against wall lines.
Body size is the separate axis. A compact body drops into a single ceiling tile and suits small rooms and shallow voids. A full-size body carries more capacity, and asks for more depth above the ceiling to sit in.
| Format | Where it usually goes | What it changes for the occupant |
|---|---|---|
| FormatFour-way blow | Where it usually goesSquare rooms, open offices, larger condo living areas | What it changes for the occupantEven spread from a central position, and four vanes to keep moving |
| FormatTwo-way blow | Where it usually goesLong narrow rooms, corridors, meeting rooms | What it changes for the occupantAir runs along the room rather than into the nearest walls |
| FormatOne-way blow | Where it usually goesSmall rooms and positions tight against a wall line | What it changes for the occupantDirectional coverage, so furniture placement matters more |
| FormatCompact body | Where it usually goesBedrooms, small offices, shallow ceiling voids | What it changes for the occupantDrops into one tile, with a smaller filter and a smaller tray |
| FormatFull-size body | Where it usually goesOpen floors carrying a heavier cooling load | What it changes for the occupantNeeds deeper void, and reaching the far side of it takes more room above |
Six things worth knowing about your own unit
None of this requires opening anything. All six can be established from the floor, and having them ready shortens any conversation about the unit later.
The last one earns its place because it is the one occupants can change by accident. A cassette that cooled a space properly on day one and struggles now, with nothing wrong inside it, has usually had its return path built over.
- How many sides the panel blows from, and whether every side is still moving air.
- Whether the ceiling around it is a suspended tile grid or solid plaster.
- Whether an access hatch exists near the unit, and where it is.
- Where the drain water comes out at the far end of its run.
- Whether other panels in the same space run off the same outdoor unit.
- What sits directly below and around the panel that could obstruct the return path.
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