Hi all, Heard this before and don't know whether is true anot? If you seldom turn on your living hall aircon , a 3+1 system will be able to save more electrical bills . This is because when you just turn on your bed room aircon, you will be running on a system 3 compressor whereas if you are using a system 4 , by turning on just one unit, you be running on your system 4 compressor which will used up more electricity.