Multi-split vs single-split aircon

Multi split vs single split side by side

The main difference is how many indoor units share one outdoor condensing unit. Rows follow the National Environment Agency (NEA) on buying energy-efficient appliances and the Energy Label, and HDB's aircon installation guidelines.

Is a multi-split or a single-split aircon better for your home?

Neither is better in every home. It depends on how many rooms you cool at the same time, and on how many condensing units your ledge and electrical supply allow. A single split aircon gives each room its own outdoor unit, while a multi-split puts several rooms on one.

NEA's tips on buying energy-efficient appliances say an oversized unit costs more to run and may not dehumidify well because it cools too quickly, while an undersized unit does not cool or dehumidify adequately. A room with double ceiling height, full-height glass, windows facing the sun (east-west) or extra heat sources such as a bar fridge may need a larger aircon.

When one condenser serves several rooms

If you choose a multi split aircon, every room on that system shares its outdoor unit. By definition, a fault in that unit affects every room on it. With single splits, each room has its own outdoor unit, so a fault in one affects only the room it serves.

NEA's sizing advice says a multi-split's total capacity is usually the sum of the rooms' capacities, but a smaller total may be enough if all rooms are not cooled at the same time. Its rule of thumb per room is floor area in square metres divided by 5 for the kW needed; multiply that by 3,412 for British thermal units per hour (BTU/hr). For a detailed assessment, NEA says to consult your aircon supplier.

To work out each room, see aircon BTU by room size or try the aircon BTU calculator.

Ledge, weight and electrical limits in HDB flats

Under HDB's aircon installation guidelines, flat owners are responsible for their aircon's safety and stability. It must be installed by a BCA-trained air-conditioning condensing unit installer (BCA is the Building and Construction Authority), and an installation report must be submitted to the HDB Branch within 14 days after installation.

Condensing units cannot be placed along the common corridor, and the aircon ledge is only for the condensing unit. Before installing, the owner and installer must check that the total running current of the condensing units does not exceed the approved electrical rating. HDB's rules then depend on your main switch:

• 40amps main switch, or upgraded under the Main Upgrading Programme (MUP) or Home Improvement Programme (HIP): installing an aircon on an existing or new 15A power point or 20A isolator needs no permit, subject to the guidelines. The running current is restricted by a 20A double pole isolator or 15A power point, a maximum of 2 split-type condensing units can be installed, the maximum weight is 110kg per wall panel, and a wall-mounted condensing unit allows only 1 unit per wall panel.
• 30amps main switch: a new 15A power point or 20A isolator for the aircon needs an electrical permit.

For both types, the limit counts condensing units, and a multi-split uses one for several indoor units.

Servicing and upkeep

HDB's guide to maintaining aircons says to have the condensing unit serviced regularly by a licensed service provider, and to ask whether its brackets need replacing because of rust and corrosion. Clean the air filters to keep airflow optimal.

NEA's energy saving tips add a routine: check the aircon filter once a month and clean or replace it when necessary, service aircon units regularly and get them inspected annually.

Servicing cost depends on the job; compare aircon servicing prices for your setup.

Which one should you choose?

• Rooms cooled together. If you rarely cool every room at once, NEA says a multi-split's total capacity may be smaller than the sum of the rooms.
• Main switch and ledge. A 40amps flat allows up to 2 split-type condensing units without a permit under HDB's conditions; a 30amps flat needs a permit for a new 15A power point or 20A isolator. The ledge is only for the condensing unit.
• Outdoor units to service. One outdoor unit shared by several rooms, or one for each room.
• Unit type. Compare aircon types and decide whether you want an inverter or non-inverter aircon.

Before you book, read about aircon installation and ask each installer how they sized every room and how many condensing units they propose. Installation cost depends on the job; see aircon installation cost in HDB flats.

Questions