The right air conditioner size comes down to room size first. Get that wrong and nothing else matters. After that, energy efficiency class and unit type are the two decisions that shape your running costs and daily comfort.
An undersized unit runs constantly and never quite cools the room. An oversized one short-cycles, wastes electricity, and leaves the air humid. Both mistakes are avoidable.
Start with cooling capacity, measured in BTU. A rough but reliable guide: 9,000 BTU handles a room around 20 m² (215 sq ft), 12,000 BTU covers 30, 35 m², and anything above 50 m² typically needs 18,000 BTU or more. Rooms with high ceilings, lots of south-facing windows, or poor insulation should size up one step.
Next, check the energy efficiency rating. Higher-rated models cost more upfront but cost less to run every day. If you're using the unit daily through summer, the savings add up fast.
Then decide on unit type. The most common options are:
- Fixed split system: an indoor unit paired with an outdoor compressor. The standard choice for permanent installation in one room. Quiet and efficient.
- Multi-split system: one outdoor unit connected to several indoor units across multiple rooms.
- Portable unit: no installation needed. Good for rentals or occasional use, though generally less efficient than split systems.
Once you've settled on type and capacity, look at the features. Modern air conditioners come with modes that make a real difference day to day:
- Dehumidify mode: removes moisture from the air without aggressive cooling. Useful on humid days when the temperature alone isn't the problem.
- Sleep mode: gradually adjusts temperature and fan speed overnight so you're not woken up by cold blasts or noise.
- Inverter technology: the compressor varies its output rather than switching on and off at full power. Quieter, more efficient, and gentler on the unit itself.
Noise level matters more than most people expect, especially for a bedroom. Look for units rated below 35 dB(A) on the indoor side. That's roughly the level of a quiet library.
Finally, installation position affects how well the unit actually works. A correctly placed indoor unit distributes cool air evenly across the room. A poorly placed one creates hot and cold spots regardless of capacity.
Choosing the right air conditioner means matching capacity, efficiency, and features to your specific space. Take 10 minutes to measure the room and read the energy label before you buy. You'll spend the rest of the summer glad you did.