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What Is Heat Mode In My AC System? Symbols, Costs & Fixes

Australia can get surprisingly cold in winter, and because so many people now work from home, many of us are turning to our air conditioners to warm us up.

But how does this work exactly? What is heat mode in your AC system?

What is heat mode in my AC system?

Heat mode is when an air conditioner produces warm air. It does this using reverse cycle technology which reverses the refrigeration cycle in the system. This works in the following way:

A cold liquid called refrigerant passes through an external coil, absorbing heat from the air outside.

  1. The refrigerant is pumped by a compressor down through chambers and into a condenser.
  2. As the refrigerant is compressed, it warms up, creating hot air.
  3. This hot air is pushed into the room by a fan to warm the area.

When functioning in regular cool mode, the flow of refrigerant is reversed in the system.

The beauty of a reverse cycle air conditioner is that it can cool you down in the summer, and warm you up in the winter. This is especially useful for colder parts of Australia like Melbourne and Adelaide, where scorching summers and cold winters are common. They are also a great way to save money and space in your home, because you won’t need to buy individual heaters for each room, and you won’t need to place them anywhere. On the downside, they have a much higher upfront cost compared to heaters, and they can be on the noisy side. But the positives definitely outweigh the negatives. Thankfully most modern air conditioners have reverse cycle technology.

In some air conditioners (such as certain Mitsubishi units), you can also produce warm air by setting the unit to “auto mode.” This setting will either use cool or warm air depending on the system’s temperature setting compared to the temperature of the room. Once the desired temperature is achieved, the system’s inverter will stop.

What is the AC heat mode symbol?

The AC heat mode symbol is usually depicted as a sun, but differs slightly depending on the system’s manufacturer. Some opt for the word “HEAT” instead. Both are obvious and easy to remember when your toes feel like they’re about to fall off.

Here are the various heat mode symbols that you can expect to see on your remote or wall-mounted controller, based on the best quality AC systems:


AC heat mode symbol or word







How to activate heat mode for your AC

To activate heat mode for your AC, simply press the sun icon button, the “HEAT” button, or whichever button is relevant on your remote or wall controller. The AC system will likely stop, spend a few minutes reversing the refrigeration cycle, and then start producing heat.

What AC temperature should I set for heat mode?

The average temperature you should set for heat mode is 19°C, but this changes depending on which state you live in. As you might expect, the cooler your state, the higher the temperature should be set, but this only really changes by a few degrees.

Here’s a breakdown of optimal heat mode temperatures broken down by state:


Optimal heating temperature

North QLD, North WA, NT, and central Australia





19°C to 20°C







South VIC


How much does your AC’s heat mode cost?

An air conditioner’s reverse cycle function costs anywhere between $0.13 to $0.36 per hour to run. This is substantially cheaper than gas heaters ($0.43 to $0.51 per hour) and electric heaters ($0.50 to $0.60), making it a clear winner when trying to keep electricity costs down. According to Canstar, a reverse cycle air conditioner can even be cheaper to run than a microwave.1

AC heat mode not working—how to fix

If your AC’s heat mode isn’t working, it could be due to a variety of issues:

The system needs to be fixed—if all else fails, you probably need an air conditioning technician to take a look. A part may have failed in the system.


  1. Megan Birot, 2020, How to Use Your Air Conditioner for Heating, Canstar Blue