Single split vs multi-split air conditioning

The basic difference

A single split system pairs one indoor unit with one outdoor unit. A multi-split connects two or more indoor units, each in its own room, to one larger outdoor unit. Both are air-to-air heat pumps, so both heat and cool.

The choice usually comes down to three things: how many rooms you want to cover, how many outdoor units you are allowed and have room for, and how much you mind one fault affecting several rooms at once.

The planning limit that often decides it

Under Class G of the permitted development rules in England, a semi-detached or terraced house, or a block of flats, can have only one air source heat pump outdoor unit without planning permission. A detached house can have two. This changed on 29 May 2025, when the limit for detached houses rose from one to two.

That makes the choice simple for many homes. If you live in a semi or terrace and want three bedrooms cooled, three single splits would need three outdoor units and a planning application. A multi-split covers all three rooms from one outdoor unit and can stay within permitted development, provided it passes the other tests, including the 37 dB(A) noise limit under MCS 020 a).

Much of Leeds is semis and terraces, and the council counts about 19,500 pre-1919 back-to-back houses alone. For those homes, a multi-split is usually the way to cover more than one room.

Single split: strengths and limits

A single split is the simplest system. It suits one room, or homes where each room can have its own outdoor unit.

• Usually the lowest cost for one room.
• Each system is independent, so a fault affects one room only.
• Each room can heat or cool regardless of the others.
• Simpler to fit and service.
• Every extra room needs another outdoor unit, which planning limits and wall space restrict.

Multi-split: strengths and limits

A multi-split puts several rooms on one outdoor unit. Each indoor unit has its own controls, so you can run one bedroom and leave the others off.

The compromises are worth knowing about. On most standard multi-splits, all the indoor units have to be in the same mode, so one room can't heat while another cools. If the outdoor unit develops a fault, every room it serves goes off together. The outdoor unit is larger and heavier, so its position needs to suit it. Pipe runs from the outdoor unit to each indoor unit have length limits, which the installer checks at survey.

Servicing also takes longer, since there are several indoor units, though there is still only one outdoor unit to check.

Sizing a multi-split: a worked example

Each room still needs its own indoor unit sized for that room. Daikin's UK sizing guide gives a rule of thumb of about 0.1kW per square metre for a typical room with a 2.4m ceiling, and adds 10% to 20% for large south or west facing windows.

Take a semi in Rothwell with three bedrooms. Bedroom one is 4m by 3.5m, which is 14 square metres, so 14 x 0.1 = 1.4kW. Bedroom two is 3m by 4m, 12 square metres, so 1.2kW. The main bedroom is 4m by 5m, 20 square metres, so 2.0kW, and it faces south-west with a large window, so adding 20% gives 2.0 x 1.2 = 2.4kW. The total is 1.4 + 1.2 + 2.4 = 5.0kW.

The outdoor unit is chosen to suit that combination. Manufacturers publish which indoor units each multi-split outdoor unit can take and the combined capacity allowed. Because the rooms rarely all need full output at once, the outdoor unit's rated capacity can be less than the sum of the indoor units. That is something the installer should explain on your quote.

How the costs compare

We don't publish a fixed price for a multi-split, because it depends on the number of rooms, the pipe routes and the model. What you can do is compare.

For a single split, Checkatrade's 2026 cost guide gives national averages of £750 for a 12,000 BTU wall-mounted unit, £1,150 for labour and £400 to £700 for the electrics. That makes £750 + £1,150 + £400 = £2,300 at the low end and £750 + £1,150 + £700 = £2,600 at the high end, for one room.

Three separate single splits would mean three outdoor units, three sets of electrics and, on a semi or terrace, a planning application. Ask for a multi-split quote and, if your home allows it, a separate-units quote, and compare the total for the rooms you want. Installing an air-to-air heat pump in a home is zero-rated for VAT until 31 March 2027 under HMRC's VAT Notice 708/6, and our partner installers are MCS certified and apply the 0% rate on domestic installations.

Running costs and efficiency

Running cost depends mainly on how many rooms you run, for how long, and how efficient the system is. Compare the SEER for cooling and the SCOP for heating on the data sheets of the systems you are quoted. Daikin's guide describes a SEER of 8.5 or more as A+++ and calls a SCOP above 3.5 high performance.

Worked example for heating: at the Ofgem price cap for October to December 2026, electricity is 26.32p per kWh by Direct Debit. A system with a SCOP of 4.0 gives 4kWh of heat for each kWh of electricity, so heat costs 26.32 / 4 = 6.6p per kWh. If two bedrooms on the system need 10kWh of heat between them on a cold evening, that costs 10 x 6.6p = 66p, whether the heat comes from one outdoor unit or two. The efficiency figures on the data sheets are what change the answer, so compare them.

Controls and day-to-day use

With either system, each room gets its own remote or wall controller, and many models offer an app. On a multi-split, you can set each room to its own temperature and switch rooms off when they're empty, which keeps running costs down.

The shared mode is the one thing to plan around. In spring and autumn, a sunny south-facing room may want cooling while a north-facing room wants heat. On a standard multi-split you pick one mode for the whole system. In practice most households set it to heat from autumn to spring and cool in summer, and it rarely causes problems. If you know you have rooms that behave very differently, mention it at survey.

Ducted and concealed options

If you don't want a unit on each wall, ducted indoor units can sit in a loft or ceiling void and feed air through grilles. They can be used with some multi-split outdoor units. Checkatrade's 2026 guide lists ducted labour at an average of £1,750 per unit, against £1,150 for a wall-mounted unit, and notes that ductwork and fittings are extra. They are usually easier to fit during other building work, such as a loft conversion.

Which to choose

For one room, a single split is almost always right. For two rooms, it depends on the house: on a detached house you could have two singles under permitted development, while on a semi or terrace a two-room multi-split keeps you to one outdoor unit. For three or more rooms on most Leeds houses, a multi-split is usually the practical choice.

If you might add rooms later, say so at survey. Some multi-split outdoor units take additional indoor units up to a limit, but only if the outdoor unit was chosen with that in mind.

For larger commercial buildings with many zones, VRF systems take the same idea further. Our commercial page covers those.

Where the outdoor unit goes

A multi-split outdoor unit is bigger than a single split one, so check the volume against the 1.5 cubic metre permitted development limit for houses, or 0.6 cubic metres for a block of flats. The data sheet gives the dimensions, and the volume is width x height x depth.

In Leeds's 80 conservation areas, the unit can't go on a wall or roof facing a road. On a back-to-back, where the only outside wall often faces the street, that may rule out permitted development entirely, and a planning application is the next step. Our planning guide sets out the rules in full.

Sources

• GPDO 2015, Schedule 2 Part 14
• Daikin UK, Air conditioner size guide
• Checkatrade, Air conditioner installation cost breakdown 2026
• MCS 020 a) sound calculation
• Leeds City Council, Leeds Housing Strategy
• HMRC, VAT Notice 708/6: energy-saving materials and heating equipment
• Ofgem, Energy price cap unit rates and standing charges
• Leeds City Council, Conservation areas