How to Choose the Right Size Air Conditioner for Your Room
Buying the wrong size air conditioner is one of the most common mistakes Australian homeowners make. Too small and it struggles to cool the room. Too large and it short-cycles — switching on and off constantly, using more electricity and failing to dehumidify properly. Here's how to get it right.
The Basic Sizing Rule
Air conditioner capacity is measured in kilowatts (kW). As a starting point:
- 10m²–20m² (small bedroom): 2.0–2.5kW
- 20m²–40m² (large bedroom, small lounge): 2.5–3.5kW
- 40m²–60m² (open-plan kitchen/living, large lounge): 4.0–5.0kW
- 60m²‐80m² (large open-plan area): 5.0–7.0kW
- 80m²+: Consider ducted or multi-split system
These are starting points only. Several factors can increase or decrease the required capacity significantly.
Factors That Increase Required Capacity
1. High Ceilings
Standard calculations assume 2.4m ceilings. If your ceiling is 3m or higher, add 20–30% to the capacity. A room with 3m ceilings effectively has 25% more air volume.
2. Poor Insulation
Older homes, homes with no ceiling insulation, or rooms with large uninsulated windows or skylights need more capacity. Add 20–30% if insulation is poor.
3. Western or Northern Exposure
Rooms facing west or north receive significantly more direct sunlight, especially in summer afternoons. Add 15–25% for heavy sun exposure without effective external shading.
4. Open-Plan Layout
Open-plan spaces need to condition a larger volume of air. If your living/dining/kitchen area flows into a hallway or other spaces, factor in the connected areas.
5. High Occupancy
Each person in a room generates about 100W of heat. A home office with multiple workstations or a room that frequently hosts guests needs additional capacity.
Factors That Reduce Required Capacity
- Good ceiling insulation and double-glazed windows
- Effective external shading (pergola, veranda, external blinds)
- Rooms that are rarely used at peak heat
- Southerly-facing rooms with minimal sun exposure
Western Sydney Consideration
Western Sydney (Penrith, Parramatta, Blacktown, Liverpool) consistently records temperatures 5–10°C hotter than coastal Sydney during summer. If you live in Western Sydney, we recommend sizing up by one step — e.g., choose a 3.5kW where the chart says 2.5kW for a bedroom.
Calculating Your Room Size
To calculate room area: measure length x width in metres. For an irregular room, break it into rectangles and add them up. Don't forget to account for any adjoining areas that the air conditioner will need to condition.
What We Recommend for Common Spaces
| Space | Typical Size | Recommended kW |
|---|---|---|
| Standard bedroom | 12–16m² | 2.0–2.5kW |
| Master bedroom | 18–25m² | 2.5–3.5kW |
| Living room (single) | 25–40m² | 3.5–5.0kW |
| Open-plan kitchen/living | 45–70m² | 5.0–7.1kW |
| Apartment (all rooms) | 50–80m² | Ducted or multi-split |
Need Help Choosing?
At Oceania Appliances, we're happy to help you calculate the right capacity for your space. Call 0450 700 001 with your room dimensions and we'll give you a recommendation. We carry a wide range of Daikin, Mitsubishi Electric, Fujitsu, LG and Samsung split systems — new and used — delivered free across Sydney. Browse at oceaniaappliances.com.au.