Cassette, ducted or wall-mounted air conditioning?
Updated 23 October 2026 · SEO Dons Editorial
How do the main indoor unit types differ?
The type is chosen room by room, and on many multi-split and VRF ranges a mix can share one outdoor unit. LG's UK page, for example, says "One outdoor unit is all you need to accommodate a diverse selection of indoor units". Daikin groups its own indoor units as ceiling cassettes, concealed ceiling units and "other models" that are wall-mounted, ceiling-suspended or floor-standing.
| Type | Where it sits | How the air arrives | What it needs |
|---|---|---|---|
| Wall-mounted | High on a wall | From one side of the room | A clear wall, a condensate route, no ceiling void |
| Four-way cassette | In a suspended ceiling | From the middle of the room, in several directions | A void above the ceiling and an access route |
| One-way cassette | In a suspended ceiling | In one direction | A shallower void, for narrow rooms or corridors |
| Ducted (concealed) | In the ceiling void or a plant space | Through ductwork to grilles or diffusers | A void for the unit and ducts, and design work for the layout |
| Ceiling-suspended or floor-standing | Under the ceiling or on the floor | Across the room from low or high level | Wall or floor space and no void |
Daikin says wall-mounted units are "Ideal for renovations and updates" and easy to install, and describes floor-standing units as "Ideal for situations when heating is your primary need". It says concealed units suit "buildings with false ceilings" and are "virtually invisible". LG says its one-way cassette "takes up minimal space, enabling flexible installation even in areas with limited ceiling space". These are makers' descriptions of their own ranges, not a comparison of makers.
How do air distribution and comfort differ?
Where the air lands matters as much as how much of it there is. The HSE lists air movement among the six factors in thermal comfort and notes that "small air movements in cool or cold environments may be perceived as a draught as people are particularly sensitive to these movements". It also says "moving air in warm or humid conditions can increase heat loss through convection without any change in air temperature".
So the same unit can feel right in one seat and wrong in the next. A wall unit above a row of desks, a four-way cassette over a meeting table and a ducted diffuser beside a window each put air in a different place. Ask the designer to show supply positions against desks and seating, and not only to state room temperature. The legal side of temperature is in workplace temperature law.
What do the noise and airflow figures on a datasheet mean?
Under the ecodesign rules retained in Great Britain, a "sound power level" is "the A-weighted sound power level [dB(A)] indoors and/or outdoors measured at standard rating conditions for cooling". The "nominal air flow rate" is the airflow "measured at the air outlet of indoor and/or outdoor units". Those definitions sit in a regulation that covers air conditioners "with a rated capacity of ≤ 12 kW". For larger equipment the 2016 regulation uses the same idea, with standard rating conditions used "to determine their rated heating capacity, rated cooling capacity, sound power level".
Two practical points follow. First, compare figures measured on the same basis, and for the same fan speed. Second, a test-condition figure is not the level in your room, which also depends on distance, room finishes and how the unit is installed. Ask for the predicted level in each room, and see air conditioning noise and noisy air conditioning for the outdoor side.
What ceiling void and access does each type need?
Void. Cassettes and concealed units need a void above the ceiling, and its depth is set by the model, so read the unit height and clearances in the datasheet and installation manual before committing. Daikin says its fully flat cassette "Integrates fully flat into standard architectural ceiling tiles", which is the kind of detail that decides how a ceiling looks. Daikin also quotes an "ESP", external static pressure, "from 10Pa to 270Pa" across its concealed range. ESP is the pressure available to push air through ductwork and grilles, so it has to be matched to the duct design.
Access. Filters, condensate pumps and coils need to be reached. The Work at Height Regulations require every employer to "ensure that work is not carried out at height where it is reasonably practicable to carry out the work safely otherwise than at height", so ask how a unit above a ceiling will be serviced and whether the layout allows safe access. The cleaning routine is in commercial air conditioning cleaning, and condensate pumps are in condensate pumps.
Ductwork. A ducted layout brings in duct leakage, cleaning and dampers, covered in DW/144 duct leakage and dampers explained. BESA says its TR19 Air specification covers "standards for the cleanliness of ventilation systems in commercial and public buildings". Where no void or outside wall is available, through-wall units are another route.
Which unit suits which room? A quick guide
This is a starting list for discussion with a designer, not a rule.
| Room | Often considered | Check first |
|---|---|---|
| Open-plan office with a suspended ceiling | Four-way cassettes, or ducted | Grid layout, void depth, supply positions over desks |
| Cellular office or small meeting room | Wall-mounted, or one-way cassette | Wall space, noise at head height |
| Shop sales floor | Cassettes, or ducted with diffusers | Appearance, shelving, out-of-hours working |
| Restaurant or café dining area | Cassettes, or ducted | Draughts at tables, condensate routes |
| Reception or boardroom where appearance leads | Ducted (concealed) | Void for ducts, grille positions, duct cleanliness |
| Space with no void and a heritage setting | Wall, floor-standing or through-wall | Consents (see listed buildings) |
Entrances are usually a separate problem, covered in air curtains, and server rooms are different again (see server room cooling). Retail and office specifics are in retail air conditioning and office air conditioning.
What should a quote say about the indoor units?
- The unit type and model for every room, and why.
- Sound power level and predicted level in the room, at the fan speed assumed.
- Airflow, supply positions and the distance air is expected to travel.
- Void depth, clearances and the route to reach each unit for service.
- The condensate route for each unit.
The commercial air conditioning cost guide publishes the installed price ladder and prices a ceiling cassette above a wall-mounted unit, so no prices are repeated here. Where several indoor units share one outdoor unit, split, multi-split or VRF explains the limits. Readers can send an enquiry through the site's form.
Sources
- VRV, Daikin UK, for facts about Daikin products, checked 22 October 2026
- Multi Split, LG Electronics UK, for facts about LG products, checked 22 October 2026
- Thermal comfort, Health and Safety Executive, checked 22 October 2026
- Commission Regulation (EU) No 206/2012, article 1, legislation.gov.uk, as retained in Great Britain, checked 22 October 2026
- Commission Regulation (EU) No 206/2012, annex I, legislation.gov.uk, as retained in Great Britain, checked 22 October 2026
- Commission Regulation (EU) 2016/2281, article 2, legislation.gov.uk, as retained in Great Britain, checked 22 October 2026
- The Work at Height Regulations 2005, regulation 6, legislation.gov.uk, checked 22 October 2026
- TR 19 Internal Cleanliness of Ventilation Systems, BESA Publications, March 2026 edition, checked 22 October 2026
- Checking F gas equipment for leaks, Environment Agency and Defra via GOV.UK, published 21 August 2019, checked 22 October 2026
Common questions
Is a ducted system quieter than a wall-mounted one?
Not by type alone. A ducted unit sits out of sight, but its noise depends on the model, the fan speed and the duct design. Compare sound power levels measured on the same basis, then ask for the predicted level in the room.
Can cassettes be fitted without a suspended ceiling?
Cassettes are made for ceiling voids, and Daikin says its fully flat cassette integrates into standard ceiling tiles. Without a void the options are usually wall-mounted, ceiling-suspended or floor-standing units, or a different route such as through-wall units.
Does the indoor unit type change the refrigerant or leak-check rules?
No. GOV.UK says how often leaks must be checked depends on the amount of F gas in the equipment and its global warming potential. The style of indoor unit does not change that.
Why does the same temperature setting feel different under different units?
The HSE says air temperature alone is not a valid or accurate indicator of comfort, and that air movement is one of six factors. Where the supply air lands relative to people changes how a setting feels.
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