Split air conditioning explained: single split, multi-split and ducted

What split air conditioning means

Every air conditioner moves heat with a refrigerant, a compressor and two coils. A split system puts the noisy parts, the compressor and the big fan, in an outdoor unit. The room only gets a quiet indoor unit with a coil, a fan and filters. Two insulated copper pipes carry the refrigerant between them, with a cable and a drain, through one hole in the wall.

The government's F-gas guidance describes a single split as a system with one cooling coil connected to a remote condensing unit. The alternatives are one-box units: a portable on the floor, or a through-wall unit with two grilles outside. Both keep the compressor in the room with you, which is why split systems are quieter and more powerful.

Most split systems sold for homes are reversible: a valve changes the direction the heat moves, so the same system heats in winter. That makes them air-to-air heat pumps, and every home system we fit works this way.

Mini split, ductless and split AC: the same thing

If you've read American sites, you'll have seen "mini split" and "ductless". The US Department of Energy calls these systems ductless mini-split heat pumps. They're called ductless because the indoor unit blows air straight into the room instead of through ducts.

In the UK the same thing is just called a split system, a split AC unit or wall-mounted air conditioning. The products are the same families from the same manufacturers. One difference to watch: US articles quote sizes in BTU and prices in dollars, and their planning and electrical rules don't apply here.

Single split, multi-split and ducted compared

How many rooms can one outdoor unit run?

On home multi-splits, up to five or six. Daikin says up to five indoor units can be connected to its 5MXM outdoor unit, and that they don't need to be installed at the same time, so a room can be added later if the outdoor unit was chosen for it. Mitsubishi Electric's MXZ-F range runs up to six indoor units, in sizes from 3.3 to 12.2 kW, and lets you mix wall, floor, cassette, ducted and ceiling units on one system.

Pipe limits set the layout. Daikin's 5MXM90A allows up to 25 m of pipe to any one room, 75 m in total, and 15 m of height between the outdoor unit and an indoor unit. In practice, beyond four or five rooms a second system is often the better design, and we check the limits against your real pipe routes at the survey.

Single split: pros and cons

A single split is one room's system. It's the cheapest way to cool and heat one room, and the most efficient, because the outdoor unit is matched to that one indoor unit.

• Lowest price for one room: from £1,850 inc. VAT for a 2.5 kW bedroom unit
• Each system is independent, so a fault only affects one room
• One room can heat while another system cools
• Most single-room installs take a day
• But each room needs its own outdoor unit, which takes wall space and counts towards the planning limit

Multi-split: pros and cons

A multi-split trades a little flexibility for a much tidier outside wall. Mitsubishi Electric's service manual explains the main catch: if one room asks for cooling and another for heating, the room that started first sets the mode and the other waits until they match.

• One outdoor unit for two to five or six rooms, which keeps the back of the house tidy
• On a semi, terrace or block of flats, it keeps you within the one heat pump allowed as permitted development
• Each room still has its own unit, remote and temperature
• Usually a little cheaper than the same number of single splits
• But every room stops if the outdoor unit fails, and all rooms run in the same mode
• Running one small room on a big outdoor unit is usually a little less efficient than a single split

Ducted split: hidden indoor unit

A ducted system is still a split system. The indoor unit sits out of sight in a ceiling void, loft or bulkhead, and insulated ducts carry the air to slim grilles. You see grilles and a controller, nothing on the wall. It needs space above the ceiling and an access hatch for servicing, so it's best fitted during a loft conversion, extension or refurbishment. Our ducted air conditioning page has the details.

What each type of split system costs with us

Home prices, including VAT, for a standard install with up to 5 m of pipe per room, the outdoor bracket, commissioning and warranty registration. Ducted systems are always priced after a survey.

• A bedroom or study

  2.5 kW wall unit, 5 m pipe, fitted in a day

  from£1,850inc. VAT

• A living room

  3.5 kW wall unit

  from£2,050inc. VAT

• Open plan or a loft

  5 kW wall unit

  from£2,450inc. VAT

• Two rooms, one outdoor unit

  Multi-split

  from£3,650inc. VAT

• Three rooms

  Multi-split

  from£5,100inc. VAT

• Four rooms

  Multi-split

  from£6,500inc. VAT

• Ducted, per zone

  Hidden in the ceiling, survey needed

  from£4,950inc. VAT

Heating and efficiency: SCOP and SEER

SCOP (seasonal coefficient of performance) is the heat a system delivers over a heating season divided by the electricity it uses. SEER is the same for cooling. Both are on the energy label, which runs from A+++ to D. Panasonic's spec sheets give its premium Etherea a SCOP of 5.2 and its value-range TZ 4.6.

At the Ofgem cap for October to December 2026, 26.32p per kWh of electricity, a SCOP of 5.2 means heat for about 5.1p per kWh, and 4.6 about 5.7p. A plug-in electric heater costs 26.3p. Daikin rates its 5MXM multi-split outdoor unit up to A+++ in cooling and A++ in heating. Our running costs guide has the hour-by-hour figures.

R32 refrigerant and the F-gas rules

Current home ranges such as Daikin's Perfera and 5MXM and Mitsubishi Electric's MXZ-F use R32. Daikin lists its global warming potential as 675, and says it cuts environmental impact by 68% compared with R-410A, the refrigerant many older systems use. Since 2025, new single split systems holding less than 3 kg of refrigerant can't be sold in Great Britain with a refrigerant whose global warming potential is above 750.

R32 is mildly flammable, so manufacturers set minimum room sizes and installation rules for it in their manuals. Working on these systems is controlled by law: the government says it's against the law to work with F gas without the right certification. Our engineers are F-Gas and REFCOM certified.

Planning: why the number of outdoor units matters

In England, a heating-capable split system on a house is usually permitted development under Class G, but Class G counts heat pumps. A semi-detached or terraced house, or a block of flats, can have one; a detached house can have two. Each outdoor unit is one heat pump.

So two rooms on two single splits on a semi or terrace means a second heat pump, which needs a planning application. A multi-split serving both rooms from one outdoor unit stays within the limit. If you already have an air-to-water heat pump for your radiators, any air conditioning outdoor unit is a second one.

The outdoor unit must also be no bigger than 1.5 m³ on a house or 0.6 m³ on a block of flats, and pass the MCS 020(a) noise calculation of 37 dB(A) at a neighbour's window. Even a five-room Daikin 5MXM90A is 734 by 974 by 408 mm, about 0.29 m³. Units that only cool aren't covered, and conservation areas and listed buildings have extra rules: see our planning permission guide.

Which split system should I choose?

• One room you use a lot, such as a bedroom or home office: a single split
• Two to four rooms in a semi, terrace or flat: usually a multi-split, to keep to one outdoor unit
• Rooms at opposite ends of a detached house: two single splits can be permitted development there
• You need one room heating while another cools: separate single splits
• A loft conversion or extension with ceilings still open: consider ducted
• A loft room with sloping ceilings: a floor console on a single or multi-split
• You plan to add a room later: a multi-split outdoor unit chosen with spare capacity

Split air conditioning questions