Is Ducted or Split System Air Conditioning Cheaper to Run?

The Answer: It Depends on How You Use It

There is no universal answer. A split system cooling one bedroom is far cheaper to run than a ducted system conditioning the whole house. A well-zoned ducted system with only two zones active can approach the efficiency of running two split systems simultaneously.

How Efficiency Is Measured — COP and EER

• COP (Coefficient of Performance): Heating output ÷ electrical input. A good modern reverse-cycle system has COP 4.0+, meaning for every 1kW of electricity you get 4kW of heating.
• EER (Energy Efficiency Ratio): Cooling output ÷ electrical input. Good: 3.5+.

A unit with COP 5.0 vs COP 3.8 on the same 2.5kW load saves $80–$120/year at typical Australian tariffs. Over 10 years, that's $800–$1,200 — worth factoring into brand selection.

Real-World Annual Running Cost Estimates

At $0.30/kWh (approximate mid-range Australian residential tariff):

• 2.5kW bedroom split, 8hrs/day in summer: ~$150–$250/year
• 5kW lounge split, 6hrs/day summer + 4hrs/day winter: ~$300–$500/year
• 14kW ducted (all zones open, 6hrs/day summer): ~$800–$1,400/year
• 14kW ducted (2 of 4 zones active, same usage): ~$400–$700/year

Zoned Ducted — The Best of Both Worlds?

A well-designed zoned ducted system lets you close off unoccupied rooms. If you typically only use 2 of 4 zones, a zoned ducted system can approach the running efficiency of 2 separate split systems — while providing whole-home comfort when you want it.

The key is actually using the zoning. A ducted system with all zones permanently open conditions the whole house even when you only need one room — at that point, a targeted split system wins on running cost every time.

Solar Integration Changes the Equation

If you have solar panels, the running cost comparison shifts significantly. A high-COP reverse-cycle system (4.0+) used during peak solar generation (10am–2pm) effectively runs on free energy. Supercooling — pre-cooling your home during peak solar hours and letting thermal mass hold the temperature into the evening — works particularly well with zoned ducted systems and can cut effective running costs by 50–70%.

Bottom Line

For targeted single-room cooling: split system wins on running cost. For a whole home you discipline yourself to zone correctly: ducted can be comparable. For households that leave air conditioning running all day for the whole house: a well-designed zoned ducted system may actually cost less than running 4+ individual splits simultaneously.