Air Conditioner Energy Consumption: What Your System Really Draws

What Does the kW Rating Actually Mean?

When an HVAC installer quotes you a "16kW system" (whether ducted, multi-head split, or wall-mounted) that 16kW is the cooling output, how much heat it removes from your home. It's not how much electricity it draws.

A 16kW system actually uses about 5kW of electricity to produce that 16kW of cooling. This is actually the sensible way to rate heat pumps because it measures what you get, and allows comparison with traditional heaters where input equals output. But it does catch people out when sizing batteries.

This is because modern inverter systems (ducted or split) are heat pumps. They move heat rather than generating it, making them 3-4x more efficient than direct electric heating or cooling.

Max draw occurs during startup and extreme heat. Typical draw is once the system reaches temperature on a hot (35 degrees+) day. Mild days use significantly less.

What Is the Real-World Energy Use?

The rated power draw figures assume operation at full capacity. In reality, inverter systems rarely run at full load. They modulate continuously based on demand.

How Power Draw Varies

Factors Affecting Consumption

• Outside temperature: 40 degree day = near full load; 25 degrees = minimal
• Thermostat setpoint: Each degree lower increases consumption ~10%
• Home insulation: Poor insulation = compressor works harder
• Number of zones open: More zones = more air volume to condition
• Time of day: Afternoon peak (3-6pm) is typically worst
• Duct quality: Leaky or uninsulated ducts waste 20-30% of output

What About Winter Heating with Your AC?

In winter, your solar generation drops to 25-40% of summer output. Short days, low sun angle, and cloudy weather all contribute to this. And that's exactly when you're running your reverse-cycle system for heating.

In this scenario, your battery can't save you because there's not enough solar to charge it. You're pulling most of that heating energy from the grid regardless of your battery size.

The best winter strategy combines:

• Pre-heating - warm the house during cheap overnight rates (typically 10pm-7am) or free daytime windows
• Battery arbitrage - charge during free/cheap periods, discharge during expensive evening peaks
• Thermal mass - a well-insulated home holds warmth for hours

Is It Time to Switch from Gas Heating?

If you're reading this article because you're sizing a battery and you still heat with gas, there's an elephant in the room. Gas heating is significantly more expensive to run than reverse-cycle air conditioning, and it produces carbon monoxide that can leak into your home.

The Running Cost Difference

A reverse-cycle air conditioner is a heat pump. It moves heat rather than creating it. For every 1kW of electricity, a modern reverse-cycle system produces 3-4kW of heating. Gas heaters are only ~90% efficient, so 1kW of gas produces ~0.9kW of heat.

Winter Heating Costs: A Victorian Example

Let's compare the total cost of heating a typical Victorian home from May to September. Assumptions: 16kW reverse-cycle system running 5 hours per evening (3kW average draw = 15kWh/day), 150 days of heating season.*

*Assumptions: Gas at $0.035/MJ, electricity at $0.30/kWh, reverse-cycle COP of 3.5. Actual costs vary by usage, insulation, and tariff.
**Some energy plans offer free electricity windows (e.g., 11am-2pm). With a 13.5kWh battery, you can fully charge during this period and run your heating that evening for almost nothing.

Rebates for Ditching Gas

Several Australian states offer rebates to replace gas heating with efficient electric alternatives:

• Victoria: Up to $1,000 rebate for replacing gas heating with a reverse-cycle system (Solar Victoria program)
• ACT: Interest-free loans and rebates under the Sustainable Household Scheme
• NSW: Various council-level rebates and Energy Savings Scheme incentives

Read our full Gas Heating Replacement Guide

What Battery Size Do You Need for Air Conditioning?

Planning to run your AC from battery during evening peak hours? Here's how to size appropriately, whether you have ducted or split systems:

Quick Sizing Guide

"Minimum" assumes mild conditions. "Comfortable" handles hot days with buffer for other loads.

Continuous Power: The Hidden Limit

Here's where many people get caught: your battery's continuous power output matters as much as its capacity. A 10kWh battery with only 3kW continuous output literally cannot power a 16kW AC that draws 5kW, regardless of how full it is.

• Tesla Powerwall 2: 5kW continuous, fine for most 10-14kW systems
• Tesla Powerwall 3: 11.5kW continuous, handles larger systems easily
• BYD Battery-Box: Modular, typically 5kW per unit
• Sungrow SBR: Varies by configuration, check specs

The Bigger Picture

Getting real value from your battery isn't just about buying the biggest one. It requires four things working together:

• The right energy plan - tariff structures that reward arbitrage (buy cheap overnight, use during expensive peaks)
• Correct battery specs - matching continuous power output to your actual loads
• Proper configuration - optimised for your specific tariff, usage patterns, and goals
• Ongoing optimisation - as tariffs change and new opportunities emerge

This is what BatteryIQ helps with: not just picking hardware, but ensuring your whole system works together.

How Do You Maximise AC Efficiency?