Cassettes, concealed ducted units and ceiling-suspended models keep air conditioning off the walls and spread air evenly across larger rooms. This guide helps you work out which one your space can take.
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A ceiling air conditioning unit is any indoor unit that lives in or on the ceiling instead of the wall. There are three main types. The ceiling cassette sits flush in the ceiling with a visible grille. A concealed ducted unit hides entirely in the void and supplies air through grilles. The ceiling-suspended unit is fixed to the underside of a solid ceiling. Each one is the indoor half of a split, multi-split or VRF system, connected to an outdoor unit by refrigerant pipework.
You'll find them in offices, shops, restaurants and gyms, and more and more in homes with open-plan kitchens and extensions. Below we explain how each type works and what your ceiling needs before one can go in. We also cover where they beat wall units, and how to keep them running well.
A cassette is a square or rectangular unit recessed into the ceiling, with only a decorative grille showing below. Air is drawn up through the centre of the grille, through a filter and across the coil, then pushed out through slots around the edge. Four-way cassettes blow in four directions and suit the middle of a large room. Compact cassettes are sized to drop into a standard 600 × 600mm suspended ceiling grid, which is why offices like them so much. For narrow rooms or positions near a wall, one-way and two-way cassettes do the job.
A ducted unit sits fully hidden in a ceiling void, bulkhead or loft. Short runs of ductwork carry conditioned air to supply grilles or linear slots, and a return grille brings room air back to the unit. All you see are the grilles. A slim ducted unit can serve a single room or two adjacent rooms. Larger ones can handle a whole floor of a house or an open office.
Sometimes called under-ceiling units, these fix to the underside of the ceiling and throw air horizontally across the room. They are the answer when there's no void at all. Think concrete soffits, solid ceilings in older commercial buildings, or workshops and warehouses with exposed structure. Long rooms suit them well.
| Cassette | Concealed ducted | Ceiling-suspended | |
|---|---|---|---|
| What you see | Flush grille in the ceiling | Supply and return grilles only | Whole unit below the ceiling |
| Needs a ceiling void? | Yes | Yes, with space for ducts | No |
| Air distribution | Up to four directions from the centre | Wherever grilles are placed | Long horizontal throw |
| Filter access | Drop the front grille | Via return grille or access panel | Front of unit |
| Typical setting | Offices, shops, open-plan kitchens | High-end homes, boardrooms, hotels | Workshops, solid-ceiling premises |
It mostly comes down to the space above the ceiling and what the ceiling is made of. After that, we look at how pipework, drainage and access will work.
Cassettes and ducted units need enough depth above the ceiling for the unit body, its drain connection and the pipework. For many cassettes that's somewhere in the region of 250 to 300mm, and slimmer models exist. Ducted units need extra room for the ductwork and plenum boxes. We measure the void on survey and pick models that fit it.
Suspended grid ceilings are the easiest. A tile comes out, the unit hangs from threaded rods fixed to the structure above, and the grille sits in the grid. In homes, a plasterboard ceiling needs a neatly cut opening and secure fixings to the joists or slab above. Joist direction matters too, because a unit may have to sit between joists or need trimming added.
Anything hidden in a ceiling still needs servicing. With a cassette, you simply drop the grille. A ducted unit needs a properly sized access panel underneath it for the filter, fan and drain pump. Leaving that panel out is one of the most common mistakes we see in refurbishments.
Refrigerant pipes, the interconnecting cable and the drain run through the void to an external wall or riser, then on to the outdoor unit. In multi-storey buildings this is often the bit that takes the most planning.
A ceiling unit earns its place when a wall-mounted unit would struggle to reach every corner. It also wins when there's simply no wall space to spare.
A cassette discharges air from the centre of the ceiling outwards. In a large room, that usually gives more even temperatures than a single wall unit blowing from one side. Ducted systems go a step further, because you can put several supply grilles exactly where they're needed.
For many clients, looks are the main draw. A cassette grille is white and flat and lines up with ceiling tiles or downlights, so it reads as part of the ceiling. Some manufacturers offer designer grilles in other colours, and a few have flat-panel fronts that sit almost flush. Most discreet of all is a ducted system, where the only visible parts are slot diffusers that can be painted to match.
The catch is that discreet systems take more work to install. Ducted units especially are best planned at the design stage of a refurbishment while the ceilings are down. Retrofitting one into a finished room is much harder.
Condensate. Every air conditioner pulls moisture out of the air when it cools. Ceiling units usually sit at the highest point of the room, so many cassettes and ducted units include a built-in drain pump that lifts the water up and away to a suitable drain. We pipe the condensate to a gully, soil stack or waste, with falls and traps installed properly.
Fresh air. An air conditioner recirculates and conditions room air. It doesn't bring in fresh air by itself. Some cassettes have a knockout for a fresh air connection, and in commercial buildings we often pair ceiling units with a mechanical ventilation system. Our page on ventilation with air conditioning explains how the two work together.
Controls. Ceiling units are normally run from a wired wall controller. In a shared office that's tidier than a handheld remote, and much harder to lose. Larger installations can have central controllers and building management connections, which we cover on our commercial air conditioning page.
Yes, and they're turning up in more homes every year. Open-plan kitchen and living extensions are often too big, too glazed or too short of wall space for one wall unit to cope. We see plenty of these on air conditioning jobs in Jesmond. A compact cassette set into the plasterboard ceiling, or a slim ducted unit above a bulkhead, can serve the space evenly and blend into the design. The engineers at UK Aircon can also put ceiling units on the same multi-split air conditioning installation as wall units in the bedrooms, all sharing one outdoor unit.
In a home, the key questions are void depth, joist layout and whether a bedroom or bathroom above limits access. If those check out, a ceiling unit is a perfectly practical domestic option. If they don't, a wall-mounted air conditioning unit is still the simpler choice.
Ceiling units run from small domestic capacities up to large commercial outputs. The right size depends on the heat load of the space. Floor area, glazing and orientation all feed into that, along with insulation, the number of people, and the heat thrown off by computers, lighting and equipment. Busy spaces such as restaurants and gyms often need more capacity than their floor area would suggest. Our article on what size air conditioning unit you need explains the principles.
Look for inverter-driven systems with strong SEER (cooling) and SCOP (heating) figures. In commercial buildings, bear in mind that air conditioning systems with a combined effective rated output over 12kW need a TM44 energy inspection every five years. Systems holding refrigerant at or above 5 tonnes CO2-equivalent also need periodic leak checks under F-Gas rules.
Because ceiling units are out of sight, they are easy to forget about. A neglected cassette loses airflow and pushes dust into the room. It can also develop drain problems, which tend to show up as a stain on the ceiling tile.
Our air conditioning maintenance and repairs team services cassette, ducted and suspended units from any manufacturer.
A cassette is recessed into the ceiling with its grille visible and discharges air directly into the room below. A ducted unit is completely hidden in the ceiling void and delivers air through ductwork to separate supply grilles, so only the grilles are visible.
It varies by model, but many cassettes need somewhere in the region of 250 to 300mm of void depth, and slimmer models are available. Ducted units need additional space for ductwork. The void should be measured on survey before a model is chosen.
Yes, by using a ceiling-suspended unit, which fixes to the underside of a solid ceiling and throws air horizontally across the room. Cassettes and ducted units both require a void.
Condensate collects in a drain tray and is usually lifted by a built-in drain pump into pipework that runs to a suitable drain, such as a gully, soil stack or waste pipe.
Yes. Cassette, ducted and suspended units connected to a heat pump outdoor unit provide efficient heating as well as cooling.
A single cassette for an open-plan kitchen and a fit-out for a whole office floor have one thing in common: the survey decides which ceiling unit will work. Our REFCOM-registered engineers check the void, structure, pipe routes and drainage before recommending a system. Business owners can read about our commercial air conditioning installation service, and homeowners can request a free quote. Installations start from £1,800 and carry a 5-year warranty on parts and labour.
The wall-mounted split is the most common air conditioner in UK homes and small offices. Where it goes, how it is fitted and how it is set up decide how well it performs for the next decade.
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Read article : Domestic Air Conditioning: Key Systems, Maintenance Strategies, and Efficiency TipsFree, no-obligation quotes from REFCOM registered installers with over 20 years of experience. Locally owned and operated, with a 5 years warranty.
