Types of Split-System Air Conditioners and When to Use Each

Key takeaways

• Single-zone split systems suit one main room (such as a bedroom or home office), while multi-zone systems are better for whole-home or multi-room control.
• Ductless mini splits are ideal for retrofitting in UK homes without existing ductwork; ducted splits work best when you want hidden vents and consistent temperatures across multiple rooms.
• Wall-mounted indoor units are the default choice for most homes; floor consoles and ceiling cassettes help in awkward spaces like loft conversions or rooms with little wall space.
• Inverter and heat pump models, such as compact wall splits in the 12,000–18,000 BTU range, offer efficient year-round heating and cooling when sized correctly for the room.
• For a balanced option that can heat and cool a typical living room efficiently, an inverter wall split heat pump like the Senville LETO Series wall split is often a strong starting point.

What is a split-system air conditioner?

A split-system air conditioner has two main parts: an indoor unit that blows cooled (or heated) air into the room, and an outdoor unit that rejects the heat outside. They are connected by insulated refrigerant pipes and a power/control cable, rather than a big flexible hose through an open window.

Because the noisy compressor sits outdoors, split systems are typically quieter and more efficient than portable or window units. They often double as heat pumps, providing heating as well as cooling, which can be attractive in milder UK seasons where full central heating is not needed all day.

Single-zone vs multi-zone split systems

One of the first distinctions to understand is whether you need a single-zone or multi-zone system. This determines how many indoor units are connected to each outdoor unit and how you control the temperature in different parts of your home.

Single-zone split systems

A single-zone split system has one outdoor unit connected to one indoor unit. It is sized for one room or a clearly defined open area. Most of the compact wall-mounted systems you see advertised for bedrooms or home offices are single-zone minisplits.

Single-zone systems are ideal when you want targeted comfort:

• Bedrooms and nurseries – Quiet operation and consistent temperature through the night.
• Home offices – A cool workspace without overcooling the rest of the house.
• Loft conversions – Where heat can build up under the roof and other cooling methods struggle.

A typical example is a 12,000 BTU inverter wall split with heat pump functionality, similar in concept to the Senville LETO Series inverter wall unit. A system like this can comfortably serve an average UK double bedroom or small living room when properly sized.

Multi-zone split systems

A multi-zone (or multi-split) system connects several indoor units to one outdoor unit. Each indoor unit usually has its own thermostat and controls, so you can set different temperatures in different rooms while sharing the external hardware.

Multi-zone systems are particularly useful when:

• You want to cool multiple bedrooms upstairs with separate controls.
• You have a large open-plan living/kitchen area plus a separate snug or office.
• You are looking to replace or supplement central heating with a more efficient heat pump system.

The main trade-off is complexity and cost. Multi-zone systems require careful design so the outdoor unit can handle the combined load, and the pipe runs must be planned to each indoor unit. For a detailed comparison of costs and pros/cons, you may find it helpful to read this dedicated single-zone vs multi-zone guide.

Real-world UK layout examples

Consider a typical UK three-bed semi-detached home:

• Scenario A – One hot bedroom: The main problem is one south-facing bedroom that gets uncomfortably warm. A single-zone wall-mounted split is often the simplest solution.
• Scenario B – Upstairs feels stuffy: All three bedrooms are warm in summer. A three-zone multi-split with a small indoor unit in each bedroom gives individual control without multiple outdoor units on the wall.
• Scenario C – Open-plan ground floor: A large kitchen-diner and lounge form one big space. One larger single-zone wall-mounted unit or a ceiling cassette can handle the whole area if air circulation is good.

Ductless mini split vs ducted split systems

Another major difference between split systems is whether they use visible indoor units that blow air directly into the room (ductless mini splits), or hidden ductwork that distributes air through grilles (ducted splits).

Ductless mini splits

Ductless mini splits are the most common type in UK homes. The indoor unit is mounted on a wall, floor or ceiling and connected directly to the outdoor unit with refrigerant pipes. No large air ducts are required.

Advantages include:

• Easy retrofitting in homes without existing ducts.
• High efficiency, as there are minimal duct losses.
• Independent room control with multi-zone systems.

Many modern ductless systems also combine several functions. For example, an 18,000 BTU wall split with cooling, heating, dehumidifying, air purification and fan-only modes gives year-round flexibility. A system with around 5.1 kW capacity, Wi‑Fi control and an A++ efficiency rating, similar in concept to an 18,000 BTU 5-in-1 wall split with heat pump, can be a strong option for a medium to large living area.

Ducted split systems

Ducted split systems hide the indoor unit in a ceiling void, cupboard or loft space. Conditioned air is then distributed through ducts to vents in each room. This creates a more centralised, integrated look, similar to traditional central air, but powered by a heat pump-style outdoor unit.

They are well suited when:

• You want minimal visible units on the walls.
• Your home has accessible voids or loft space to run ducts.
• You prefer a consistent temperature across rooms rather than very different set-points.

Installation is more invasive, as it involves running ductwork and cutting vents. For many existing UK homes, especially those without generous ceiling voids, ductless mini splits are usually more practical. Where you are choosing between these and more traditional whole-house options, this comparison of mini splits vs central air explores the trade-offs in more detail.

Indoor unit types: wall, floor and ceiling

Once you have settled on single vs multi-zone and ductless vs ducted, the next decision is the style of indoor unit. This affects comfort, airflow and how the system looks in your home.

Wall-mounted units

Wall-mounted indoor units are the most common. They sit high on the wall, usually near the ceiling, and blow cooled or heated air across the room.

They are suitable for most UK rooms because:

• They are relatively easy to position on external walls.
• Airflow from a high position tends to distribute well.
• They keep furniture space free at floor level.

Models like a compact 12,000 BTU inverter wall split, such as the Senville LETO wall-mounted heat pump, usually fit neatly above door frames or wardrobes in a bedroom. Larger 18,000 BTU units, comparable to an 18,000 BTU wall split with installation kit, often suit open-plan living areas.

Floor console units

Floor console units sit low on the wall, a little like a radiator. They can be helpful where wall space up high is limited or sloped, such as in loft conversions with low eaves.

Floor units are worth considering when:

• Your room has sloping ceilings or large windows up high.
• You prefer the unit to blend in with radiators or furniture at low level.
• You want better heating comfort, as warm air can be directed from the floor level upwards.

They do take up wall space at skirting level, so you need to plan around furniture. Air distribution can be excellent for heating, while for cooling it is important that the fan and louvre design push air far enough across the room.

Ceiling cassette units

Ceiling cassette units are mounted in a suspended or false ceiling and usually blow air in two or four directions. They are common in offices and shops, but also used in some homes with suitable ceiling voids.

They are particularly useful when:

• You want to cool a large open-plan area from a central point.
• Wall space is dominated by windows, doors or kitchen units.
• You prefer a discreet look, with only a slim grille visible.

Installation is more complex and often needs more ceiling access than a wall unit. However, for kitchens and living areas in modern homes with dropped ceilings, a cassette can provide strong, even air distribution without a visible indoor unit on the wall.

As a rule of thumb, pick the unit style that works with your room’s structure first, then refine the exact size and features. Forcing an unsuitable unit type into an awkward space often leads to poor airflow and comfort later.

Inverter vs fixed-speed compressors

The compressor is the heart of any split-system air conditioner. There are two main types: fixed-speed (on/off) and inverter (variable speed). This choice affects efficiency, running costs and comfort.

Inverter split systems

Inverter systems vary the compressor speed to match the cooling or heating demand. When the room is far from the set temperature, the compressor runs harder; once it is close, it slows down to maintain the temperature gently.

Benefits include:

• Higher efficiency, especially in part-load conditions typical of UK weather.
• More stable room temperatures with fewer noticeable on/off cycles.
• Quieter operation at lower speeds.

Most modern minisplits, including units like the Senville LETO inverter wall split, use this technology. For continuous use in living areas or bedrooms, inverter systems are generally preferred.

Fixed-speed split systems

Fixed-speed compressors operate in a simpler on/off manner. They run at full power when cooling or heating is needed and switch off when the set temperature is reached.

They can have a lower upfront cost, but:

• They may use more electricity overall if cycled frequently.
• Room temperature can fluctuate more as the system overshoots slightly then turns off.
• Noise levels may be higher during each on-cycle.

In many cases, spending a little more on an inverter model pays back in energy savings and comfort over time, particularly when the system is used for both heating and cooling.

Heat pump vs cooling-only split systems

Most modern split systems for homes are reversible heat pumps: they can both cool in summer and provide heating when needed. Some very basic models are cooling-only, which might suit specific uses but are less flexible overall.

Heat pump split systems

Heat pump splits reverse the refrigeration cycle so the system can extract heat from outside air and bring it indoors. This makes them useful for:

• Supplementing radiators in rooms that feel cold.
• Transition seasons where you only need to heat one or two rooms, not the whole house.
• Year-round use, offering cooling and heating from the same wall unit.

Many 5-in-1 style systems combine heat pump heating, cooling, dehumidifying and air purification. An 18,000 BTU A++ heat pump wall split with these functions, similar in concept to this type of 5-in-1 wall-mounted heat pump, can provide a versatile solution for a main living space.

Cooling-only split systems

Cooling-only models are designed purely for warm weather. They can be simpler and sometimes slightly cheaper, but in many UK homes the extra flexibility of a heat pump is worth having. A room that overheats in summer often also feels chilly in colder months, so being able to gently warm it with the same unit is convenient.

Choosing by room type and layout

All of these types combine differently depending on where you plan to install the system. Below are some typical UK scenarios and the split-system types that tend to work best.

Bedrooms and guest rooms

Bedrooms often need quiet and precise control rather than maximum power. In most cases, the best match is:

• Type: Single-zone, ductless mini split.
• Indoor unit: Wall-mounted, high on an external wall.
• Technology: Inverter, heat pump capable.
• Size: Typically around 7,000–12,000 BTU depending on room size and insulation.

Place the unit so it does not blow directly onto the bed, using adjustable louvres to direct airflow gently. A compact inverter model similar to a 12,000 BTU LETO-type wall split is often ideal.

Open-plan living and kitchen areas

Open-plan areas are harder to cool evenly because of their size and layout. You may need:

• Type: Single-zone with higher BTU, or multi-zone if broken into clear areas.
• Indoor unit: Larger wall-mounted unit or ceiling cassette in the centre of the space.
• Technology: Inverter heat pump for efficient long-run times.
• Size: Often 18,000 BTU or higher, depending on floor area and glazing.

An 18,000 BTU ductless wall split with A++ efficiency and heat pump function, such as an 18,000 BTU wall unit with included installation kit, can often handle a typical open-plan lounge-diner, but always check room size and heat load before choosing.

Loft conversions and attic rooms

Loft rooms tend to overheat faster due to roof exposure and limited natural cross-ventilation. Structural constraints can also make unit placement difficult. Here, consider:

• Type: Single-zone ductless mini split.
• Indoor unit: Floor console against a short wall, or low wall-mounted unit under the eaves.
• Technology: Inverter heat pump with good dehumidification.

A wall-mounted unit can sometimes be positioned on a gable wall, directing air along the length of the room. Otherwise, a floor console gives more flexibility where the ceiling slopes down.

Whole-home cooling and heating

For whole-home comfort, you can either combine several single-zone systems or opt for a planned multi-zone or ducted solution:

• Multi-zone ductless – Several wall-mounted or floor units on one outdoor unit, ideal for a mix of bedrooms and living spaces.
• Ducted split – Central indoor unit feeding ducts to rooms, best where ceiling or loft space is sufficient.

If you are leaning towards multiple split systems across the home, it can be useful to cross-check sizing with a guide such as this overview of mini split sizes and BTU ratings by room.

Simple decision flow: which split-system type do you need?

While not a visual flowchart, this step-by-step logic mirrors how an installer would typically think through your needs:

1. How many spaces need cooling?
   Just one main room → Focus on single-zone ductless.
   Several distinct rooms → Consider multi-zone or multiple single-zone units.
2. Do you have space for ducts and vents?
   No or unsure → Ductless mini splits are usually best.
   Yes, with good ceiling voids/loft → Ducted split may be an option.
3. Where can an indoor unit go?
   Clear high wall space → Wall-mounted unit.
   Low walls, sloped ceilings → Floor console.
   Suspended/dropped ceiling → Ceiling cassette.
4. Do you want heating as well?
   Yes → Choose a heat pump inverter split.
   No, cooling only → Cooling-only model may suffice.
5. How sensitive are you to running costs and noise?
   Prefer quieter, efficient operation → Prioritise inverter models with strong energy ratings (A++ or better where available).

If a system choice feels marginal in terms of size or type, discuss it with a qualified installer rather than simply upsizing. Oversized systems can short-cycle, reduce comfort and may not dehumidify effectively.