Measure the space the air has to reach
In an open-plan home the living room doesn't stop at the couch. If it runs into a kitchen, a dining area or a hallway with no door, the unit is heating and cooling all of it, so measure all of it before you use the size calculator.
The kitchen brings its own load. Mitsubishi Electric says a ventilation fan or a gas cooker in the room adds to the cooling load. Solar Victoria's advice works from the other side: heat or cool only the areas you're using, and close doors where you can.
5 kW or 6 kW?
The CHOICE table that Solar Victoria reproduces gives 40 to 60 square metres a range of 4 to 6 kW, so a mid-sized living area could go either way. A higher ceiling, a sun-facing wall of glass or thin insulation all push you towards 6 kW.
Size for the harder season. Mitsubishi Electric says heating may fall short when it's very cold outside, and cooling on very hot days. The zoned energy label puts Canberra, Hobart and Melbourne in its cold zone, and the ACT Government says heating makes up about 60% of the average Canberra household's energy use. In those cities, size for a winter evening.
Victorian rentals: the living area rules
From 1 March 2027, if the heater in a rental's main living area permanently fails and can't be repaired, the replacement must be energy efficient and electric. For a split, that means a heating rating of 2 stars or above. A heater that still works can stay.
From the same date, a new or month-to-month rental agreement needs an efficient fixed cooler in the main living area: for a split, a cooling rating of 3 stars or above. Our rental rules guide has the detail.
What to ask before you settle on a size
- Did your heat load include the kitchen and the dining end?
- Where will the indoor unit go so the air reaches the far end of the room?
- Is this size chosen for winter heating or summer cooling, and how does it do in the other season?
- For a rental, what are the heating and cooling star ratings on the label?
Before the installer arrives, and after they leave
You can
- Measure the whole open area, and note which doorways you could close.
- Decide whether you mostly need it in winter or in summer.
Leave to a licensed installer
- The heat load, counting the kitchen and any open hallway.
- Positioning the indoor unit so it throws air down the length of the room.
- The licensed refrigerant and electrical work.
What we'd do
Where we'd start
Measure the whole open space, not just the lounge, and decide which season is harder in your house. If the space is close to 60 square metres, faces the afternoon sun or has a high ceiling, we'd ask a split specialist to quote 6 kW alongside 5 kW and let the heat load settle it.
