I used a calculator when we installed Fujitsu 7.4kw splits in the kitchen and dining room and a Fujitsu 3.7kw split in the master bedroom at our previous residence which seemed to fit the bill despite the “installer” saying he did not believe they would be adequate.
They were expensive to run, but the open plan kitchen, dining room and lounge room were all large and the internal staircase allowed air to spill downstairs and/or hot air to rise.
The house was on the North side of the hill and missed the prevailing breezes from the SE.
It had insulation under the colorbond but no rotary ventilators.
The house was a hot box.
When we bought our current home some 5 years ago, it already had the same aircons in the kitchen and master bedroom and a non-inverter Fujitsu split in the lounge room which promptly failed the first time we turned it on, and was replaced with the same Fujitsu split as the kitchen has.
The rooms are smaller than our previous residence, the house is single storey, there is insulation under the colorbond and Rudd’s batts above the ceiling, with 2 rotary ventilators on the roof.
The house faces South and the prevailing SE breezes come straight up the hill.
When we inspected the house before buying it, it was around 5:00 PM in mid January, and it had been locked up all day as the owner had moved out.
We could not believe how cool it was.
Even during the high heat and humidity during the past few weeks, all 3 aircons do not use more than 2kw of power in total in the middle of the day, and will be only be drawing around 1kw at cooler times.
When we get up in the morning, the bedroom aircon is usually only drawing around 200 watts or less.
So 2 different residences with exactly the same aircons but with very different efficiencies and power usuage.