Energy efficient split system air conditioners

Air conditioners get a bad rap for the load they place on the energy system. It surprises many people to learn though that they’re particularly efficient at turning energy into warmth or coolth. If you’re buying a new unit or replacing an old unit these tips will help you minimise the energy consumption and maximise the life of the air conditioner.

Buying guide

  1. Energy efficiency rating – all conditioners sold in Australia are required to be tested to against and Australian standard and labelled. Buy the most energy efficient unit you can afford, remembering that extra money spent up front will result in lower power bills in future. You can find a list of all air conditioners sorted by their energy rating at
    Note that the highest rating might not be available in all sizes of units, per below, first up ascertain what size unit is needed.
  2. Brand – as with all appliances and devices there are high end, high quality, well-known brands through to cheaper less known or less reliable brands.  Staying with well known, long-standing and reputable brands is a good approach if you’re looking for an air conditioner to last for a long time. Start with:
    samsung-logo fujitsu-logo lg-logo
    mitsubishi-logo daikin-logo panasonic-logo
  3. Inverter – most manufacturers today will offer air conditioners with inverter technology. Without an inverter, the unit will turn on to cool the air to the requested temperature then turn off, wait till it rises again then turn on again. With an inverter, the unit will start at full capacity, then when the desired temperature is approached it will slow down providing just enough cooling to maintain it. The latter approach avoids the start/stop cycles which in turn improves energy efficiency and increases the life of the machine.
  4. Sizing – this is one of the most important things to get right and is very often gotten wrong. Your air conditioner MUST be the right size in order to be energy efficient and last a long time. Too small is a problem and too big is a problem too! This is a task that really needs to be carried out by a qualified installer and is a complex topic in its own right. A few factors of the key factors are provided to give a basic understanding as to the complexity:
    • Basic split system air conditioners are designed for a single room. If you need to cover multiple rooms look at more than one system, a multi-head split system, or a ducted system. Trying to use a single head split system for multiple rooms will degrade both efficiency and comfort.
    • Most air conditioners sold in Australia are reverse cycle, meaning they can both heat and cool. Your heating loads might be larger than your cooling load or vice versa.
    • The load placed on an air conditioner is a function of
        • Air leakage / draftiness of the room. Gaps around doors, windows, floorboards etc.
        • Insulation level in ceiling, walls, floors
        • Size of the window area and types of windows
        • Area of the room being
        • How much sun  enters the room
          • Is it shaded from hot summer sun?
          • Do the external walls and windows face North? South? East? West?
          • Does the warming winter sun enter through windows?
        • The presence of window coverings both internal and external
        • What the room is made of. Is there thermal mass in the form of bricks or concrete that retain warmth or coolth?
        • How the room is used – how many people, how often they come and go etc
    • If you choose a unit that is too small:
      • You will never reach the desired temperature, in winter you might not be able to make the room warm enough, in summer not cool enough
      • But, an undersized unit will not be inefficient – it will just provide less comfort.
    • If you choose a unit that is too large:
      • You will quickly reach the desired temperature but as the unit slows down it will reach the minimum level that it can operate (typically around 20-30% of maximum). If this minimum is still too much (i.e. it’s providing more cooling or heating than required) the unit will turn off and on from time to time. A unit that is much too large will turn on and off frequently both wasting energy and be reducing the life of the machine.
  5. Replacement systems – if you’re replacing an existing unit don’t assume the right sized unit was installed in the first place. Have a reputable installer check your size requirements.
  6. Extra features – modern air conditioners often come with extras and add-ons. Some that may be worth considering are:
    • WiFi connectivity which lets you control your air conditioner via a smartphone app. On a hot day, you can turn on your air conditioner on the way home.
    • Smart Home connectivity – some may support integration with voice assistance allowing you talk to it to turn on and off.


Getting your air conditioner professionally installed is critical to ensuring it operates efficiently. Some important and simple things you should look out for and ask your installer about follow.

  • Airflow around the outdoor unit – the job of the outdoor unit is to remove heat from inside your home to cool it or add heat to warm it. It does this indirectly by exchanging heat using the outdoor air. Airflow is absolutely critical for this process to work.
    • The outdoor unit must be a sufficient distance away from the wall it is mounted against
    • There must not be other walls or vegetation immediately in front of it. The air blown by the fan must be free to escape.
  • Location of the indoor unit – this is most important for cooling. The unit should be able to blow a stream of cold air along the ceiling for the length of the room. It then falls down over the occupants. Remember – one room per split system head unit only!
  • Refrigerant pipes – these are the pipes that connect the indoor unit to the outdoor unit.
    • It’s important that they’re not too long – the closer the indoor and outdoor units the better
    • The less tight bends in the pipes the better
    • The pipes must be well insulated
    • They need to be cleaned and pressure tested after installation but before commissioning
  • Sizing – some of the factors to consider in sizing are described above but it’s your installer that should be making the recommendation. Keep in mind that it often makes sense for an installer to over-size than undersize. Undersizing you will likely call them back when the unit doesn’t provide enough coolth or warmth. Oversize and they’re unlikely to hear from you as the system will work but you’ll likely be left with higher power bills and unit that lasts a few years less than it should.

The quality of the installation is dependent both on the person that does the work and you. If you want a good quality installation, it will take longer and hence cost more. If you look for the cheapest installation you’re unlikely to get the best quality installation as the installer would go broke!

Some tips for getting a good installation:

  • Take a recommendation from the air conditioner manufacturer
  • Don’t take the cheapest quote
  • Ask them questions about sizing based on the information above
  • Once you have your three quotes – take note if all of them are not for the same size system


My advice for getting value for money on your air conditioner installation is to prioritise as follows:

  • Get the size right – too big will cost more up front and more to operate ongoing
  • Energy efficiency rating – buy the most energy efficient unit you can afford
  • Installation – get a good quality installation – avoid the cheapest quote
  • Brand – buy a well-known brand
  • Features – if you still have money left over, look at the optional extras but remember the most important feature is the heating and cooling!

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