What Is an Aircon Unit? A Complete Guide

The short answer: what an aircon unit is

An aircon unit is a machine that moves heat out of a room rather than creating cold. A refrigerant circulates through a sealed loop, picking heat up from the air inside and dumping it outside. That movement is the entire job, and it is the reason a split aircon unit always has two parts — one inside, one outside.

The cycle runs through four components. The compressor squeezes the refrigerant into a hot, high-pressure gas. The condenser coil releases that heat to the outside air and the refrigerant becomes a liquid. The expansion device drops the pressure sharply, which makes the refrigerant very cold. Then the evaporator coil pulls heat out of the room air as the refrigerant boils back into a gas, and a fan blows the now-cooler air into the room. Because it is a loop, it runs continuously while the unit is switched on.

Once you understand that, most aircon questions answer themselves. Why does the outdoor unit need space around it? Because it has to get rid of the heat it removed. Why does a blocked filter stop the room getting cold? Because the air cannot reach the cold coil. Why does low gas mean a leak? Because the loop is sealed — if refrigerant is missing, it escaped somewhere.

The two halves of a split aircon unit

The indoor unit holds the evaporator coil, a fan, the air filter and the louvres that direct the air. It is the part you see on the wall, and it is where the filter you should clean every few weeks lives.

The outdoor unit holds the compressor, the condenser coil and a second fan. It is the noisier of the two and the one that must never be boxed in, buried in shrubs or mounted facing a wall. It needs airflow across the coil, and on the coast it needs a wash-down as part of its service.

Between the two runs a line set — the copper pipes carrying refrigerant, wrapped in insulation — plus a condensate drain to carry water away and an electrical cable. The quality and length of that run matters more than most buyers realise: an over-long, uninsulated or poorly routed pipe run quietly costs you efficiency for the whole life of the unit.

The main types of aircon unit sold in South Africa

1. Split (midwall) unit — the standard. An indoor unit on the wall connected to an outdoor unit. Best for a single room, a bedroom or a small open-plan space.

2. Multi-split unit — one outdoor unit driving two or more indoor units. Useful where you want several rooms cooled but have limited space outdoors.

3. Ceiling cassette unit — a square unit set into the ceiling, blowing in several directions. A staple of shops, offices and restaurants where wall space is limited.

4. Ducted (central) unit — one larger unit hidden in the roof feeding air through ducts to outlets in several rooms. The tidiest whole-home option and the most expensive to install, because the duct design and balancing are most of the work.

5. Window unit — a self-contained unit fitted into a window or a wall opening. Cheaper and simple, but noisier and less efficient, and suited to a single room.

6. Portable unit — a movable single-room unit that needs no installation beyond an exhaust hose. The lowest entry point and the least efficient; noise is the usual complaint.

7. Floor-standing or console unit — a tall indoor unit that sits on the floor. Useful where there is no suitable wall for a midwall unit, such as a room with full-height glazing.

For a home in South Africa, the midwall split remains the default for one room and a multi-split or ducted system makes sense for a whole house. For a shop, restaurant or office, a cassette or a ducted system gives even, directional cooling that does not eat wall space.

Reading an aircon unit spec sheet

BTU and kW both describe cooling capacity. BTU stands for British Thermal Units per hour; the conversion is roughly 3,412 BTU to one kilowatt, so the numbers you see on South African listings line up as 9,000 BTU = about 2.6 kW, 12,000 BTU = about 3.5 kW and 18,000 BTU = about 5.3 kW. Model names round these figures, so a unit called 12,000 BTU may be rated slightly above or below it.

Inverter or fixed speed is the next thing to look for. A fixed-speed unit switches its compressor fully on and off. An inverter unit varies compressor speed continuously, so it holds a steadier temperature, runs quieter and uses less electricity. It costs more upfront and earns that back over a few cooling seasons in a room you use daily.

The energy label is worth a look, too. South Africa has a compulsory specification for the energy efficiency and labelling of air conditioners, so a unit lawfully sold here carries an efficiency label. Comparing labels between two units of the same capacity is a fairer comparison than comparing price alone.

Refrigerant type is the last line to check. Modern units use R32 or R290, with far lower global-warming impact than the R22 and R410A they replace. If a listing does not state the refrigerant, ask — and if you own an old R22 system, plan a replacement rather than another recharge, because that gas is being phased out.

Finally, note the indoor unit dimensions and the clearances the manual specifies. A cassette needs ceiling depth and duct space; a midwall unit needs room above it for airflow and access for servicing. Fighting the physical constraints after the fact is expensive.

How many BTU: sizing an aircon unit to a room

1. Up to 15 square metres — 9,000 BTU.

2. 16 to 25 square metres — 12,000 BTU.

3. 26 to 35 square metres — 18,000 BTU.

4. 36 to 50 square metres — 24,000 BTU.

5. Above 50 square metres — 30,000 BTU or more, often as two units.

Measure the space the unit must actually cool. If the lounge opens into the kitchen with no door, include both, because the aircon does not know where you drew the line on the plan. Then adjust for the heat factors: strong sun through large windows, high ceilings, an uninsulated roof above, a hot inland town and a humid coast all push the requirement up or change the advice.

Do not deliberately oversize. An oversized unit cools the room to the set temperature quickly, then short-cycles — switching on and off repeatedly. That wastes electricity, wears the compressor and, in humid coastal towns, leaves the room cold but clammy because the unit never ran long enough to remove moisture from the air. An undersized unit is equally disappointing in the opposite way: it runs flat out all afternoon and still never catches up. Right-sizing is the single most important decision in the whole purchase.

What is not included in the price of an aircon unit

A unit price is not an installed price, and the gap is where budgets go wrong. The box contains the indoor unit, the outdoor unit, usually a remote and a short length of pipe. It does not contain the mounting bracket or floor stand, the extra copper and insulation for a long pipe run, the trunking to hide the pipework, the condensate drain route, the electrical isolator, or an electrical Certificate of Compliance if a new circuit is needed.

It also does not contain the labour, which is the part that decides whether the unit performs as it should. Vacuuming the line set, charging to the correct weight, sealing the wall penetrations and commissioning the system are skilled work — and refrigerant handling in South Africa must be done by a technician registered with SAQCC Gas under the Pressure Equipment Regulations.

That is why the meaningful number is always the supplied-and-installed price. It is the only figure that lets you compare two quotes fairly.

Six questions to ask before you buy an aircon unit

1. Has anyone measured the room, or is this a guess from a photo and a floor area?

2. Is this price for the unit alone, or supplied and installed?

3. Is the unit an inverter, and what is its stated cooling capacity in kW as well as BTU?

4. Which refrigerant does it use, and does it carry a South African energy efficiency label?

5. What is included — bracket, pipe run length, trunking, isolator, drain, and the Certificate of Compliance if a circuit is added?

6. What warranty do I get on the unit and, separately, on the workmanship?

A company that answers all six without hesitating has done this before. One that cannot answer question one is guessing, and you will pay for the guess.

Frequently asked questions about aircon units

Q: What does an aircon unit do?

A: It moves heat from inside a room to outside. A refrigerant loop absorbs heat from the room air at the indoor coil and releases it at the outdoor coil — the unit creates cold air by removing heat, not by making cold.

Q: What is the difference between an aircon unit and an air conditioner?

A: Nothing. "Aircon" is the everyday South African term for an air conditioner, and an aircon unit is simply the appliance itself.

Q: How many BTU do I need for a 20 square metre room?

A: A 12,000 BTU unit covers roughly 16 to 25 square metres. Step up to 18,000 BTU if the room has large sun-facing windows or an uninsulated roof above it.

Q: Can one outdoor unit run several indoor units?

A: Yes — that is a multi-split system. It is often the practical answer when you want two or three rooms cooled but have space for only one outdoor unit.

Q: How long does an aircon unit last?

A: With correct sizing, a proper installation and an annual service, most split systems last well over a decade — which is why installation quality and servicing usually matter more than the badge on the front.

Get the right unit for the room, not the best-looking one

Choosing an aircon unit comes down to four things: the right capacity for the measured space, the right type for how the room is used, an inverter if the room is used daily, and an installation done properly by a registered technician. Everything else — brand, finish, remote features — is a detail on top of those.

Leon's Air Conditioning supplies, installs, services and repairs air conditioning across Kariega, Despatch, Gqeberha, Jeffreys Bay and the wider Nelson Mandela Bay region. For a no-obligation assessment, call 041 992 3363 or request a quote online.