What Size Air Conditioner Do I Need? Complete Room-by-Room Guide
Buying the wrong size air conditioner is one of the most common and expensive mistakes people make. Too small, and it runs continuously without reaching temperature, consuming energy and wearing out faster. Too large, and it short-cycles (turns on and off too frequently), creating humidity problems and uneven temperatures. This guide walks you through how to size an air conditioner correctly for your Sydney home.
The Basic Rule: Start With Room Size
The standard starting point is 125 watts of cooling capacity per square metre of floor area. So a 20m² bedroom needs approximately 2,500 watts — or 2.5kW. But this is a starting point, not a final answer. Factors below adjust the calculation significantly.
Adjustment Factors
1. Ceiling Height
Standard calculations assume a 2.4m ceiling. Higher ceilings (3m or above, common in older homes) increase the volume to cool. Add 20% capacity for ceilings above 3m.
2. Insulation Quality
Poor insulation (older homes with no ceiling or wall insulation) means more heat entry. Add 15–20% for poorly insulated rooms.
3. Sun Exposure
North and west-facing rooms receive much more direct sun. A north-facing living room with large windows requires 20–30% more capacity than a south-facing room of the same size.
4. Climate Zone
Sydney is classified as a hot climate zone. Western Sydney suburbs (Penrith, Campbelltown, Blacktown) are significantly hotter than coastal suburbs. Add 10–20% for far-western Sydney.
5. Heat-Generating Appliances
Kitchens with large ovens and stoves are significant heat sources. If you are cooling a kitchen-adjacent space, factor in this additional load.
Room-by-Room Sizing Guide for Sydney
| Room Type / Size | Recommended Capacity (Coastal Sydney) | Recommended Capacity (Western Sydney) |
|---|---|---|
| Small bedroom (up to 15m²) | 2.0 kW | 2.5 kW |
| Medium bedroom (15–20m²) | 2.5 kW | 3.5 kW |
| Large bedroom (20–30m²) | 3.5 kW | 5.0 kW |
| Living room (30–50m², good insulation) | 5.0–6.0 kW | 6.0–7.0 kW |
| Large open plan (50–70m²) | 7.0–8.0 kW | 8.0–10.0 kW |
| Office/study (10–15m²) | 2.0 kW | 2.5 kW |
Common Mistakes to Avoid
- Buying on price alone: A 7kW unit at the same price as a 5kW unit is not a bargain if your room only needs 5kW — it will short-cycle and cause humidity problems.
- Not accounting for insulation: An old, uninsulated fibro cottage needs much more capacity than a well-insulated brick home of the same size.
- Ignoring the outdoor unit location: The outdoor unit needs adequate ventilation. An outdoor unit in a confined space, in direct western sun, or above 1.5m without airflow will perform poorly.
Get Expert Advice at Oceania Appliances
Our team can help you calculate the right capacity for every room in your home. Contact us at support@oceaniaappliances.com.au or visit our Wetherill Park showroom. Open 7 days 10am–8pm. We stock Daikin, Mitsubishi Electric, Panasonic and Fujitsu across all capacity ranges.