Ceiling Cassette Aircon: What You Own Above the Grille

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.

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.

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.

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.

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.