A cassette sits in the ceiling and blows several ways, which suits an open shop or office if there is a proper void. A ceiling-suspended unit fixes under the soffit when the slab is exposed or the void is full of steel and ducts. The suspended box is visible. The cassette is only invisible if the void and the grid are real. Survey the ceiling before the brochure. Both need an outdoor unit, condensate pumping in most cases, and an F-gas installer.
Concrete you can see, or a grid with room above it
A four-way cassette wants space above the ceiling for the body, the connections and the hangers, typically a serious void rather than a plasterboard skim on battens. A 150 mm gap will not do. If the surveyor can see the concrete, you are in ceiling-suspended territory, or you build a bulkhead on purpose.
Homes rarely need either. A bedroom is almost always a wall unit. These two formats belong in retail, offices, village halls and the odd open-plan house with a commercial ceiling. Do not force a cassette into a house because a shop photo looked tidy. Daikin is one of the ranges that sells both formats. The ceiling, not the brochure, decides.
Four-way throw, a long room, and a pump
A cassette can throw in four directions and keep a square sales floor even. Corners and high racking still need a look at the plan. A ceiling-suspended unit throws along the room from one side, which suits a long narrow space and a counter on the opposite wall. The suspended unit is a piece of plant in the room. The cassette grille is quieter to the eye if the ceiling is a grid. Neither is silent, and the outdoor unit is still the neighbour issue. The Planning Portal is the outdoor-unit check. Pumps are normal. Test the drain. GOV.UK F-gas rules apply to the refrigerant circuit on either format. Energy Saving Trust describes the air-to-air heat pump that rejects heat through that outdoor condenser.
Both cost more installed than a domestic wall split of similar nameplate kW, because of ceiling work, pumps, access and usually a larger outdoor unit. Compare the same cooling duty, and leave SEER figures that are not for that exact model off the spreadsheet.
Frequently asked questions
Can I fit a cassette in a normal house ceiling?
Only with a real void or a new bulkhead. Most UK house ceilings are too tight. A wall unit is the usual domestic answer. A survey will tell you in ten minutes of looking up.
Is a ceiling-suspended unit a cassette?
No. It hangs under the ceiling instead of sitting inside it. You see the whole body. It is the right tool when there is no void.
Do these need F-gas installers?
Yes. They are split systems. Ceiling format does not change refrigerant rules.
Does a cassette in the middle cool the room behind a wall?
No. A cassette in the middle does not cool a stock room behind a wall. Corners and high racking still need a look at the plan.
Is building a void cheaper than a suspended unit?
Often no. Building a void only to hide a cassette can cost more than hanging a suspended unit under the slab. A cassette in an existing grid can be the quicker of the two.
Should I compare a smaller cassette with a larger suspended unit as a saving?
No. Compare the same cooling duty. A smaller cassette is not a saving if the door and the lighting load need the larger unit. Leave SEER figures that are not for that exact model out of it.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.