When you think about it, the 80/20, or Pareto Rule, applies here. It just simply means that 20% of the problem causes 80% of the difficulty.
Relating it to this situation, we more or less live in 20% of a home at a time, but we have to heat or cool the 80% as well. This is certainly true in homes with central heating and cooling systems, or even a stationary window air conditioner.
This is not a problem, however, with a portable A/C unit because it can easily be moved to where it is most needed. That makes them more efficient since you will only cool the area you want, thus using less electricity and making them the best portable room AC units. The newer models have variable output that compensates for the difference in use that is needed in various rooms.
For instance, some rooms have more sun coming in and other have high ceilings. If you have a portable unit, you can turn the output up and cool just the area you need without using more energy to cool the entire home with a central unit or a stationary window A/C.
An 8000 to 10,000 BTU portable unit can usually cool a room between 300 to 450 sq. ft. Units between 12,000 to 16,000 can normally cool rooms the size of 350 to 550 sq. ft. As previously mentioned, other factors in cooling a room should be considered. This may be more sun exposure, many or large windows, high ceilings, poor insulation, or skylights, and even large appliances or computers that generate heat.
Many of these units are versatile, meaning they can provide heat during cold weather as well as cooling a room in the hot summer months, and even function as a dehumidifier. It works the same way to heat an area as it does to cool the same area. The heating or cooling can be used just where needed to save energy and money.
In addition, for those who feel they cannot afford a portable ac, but would still like to have more cool air than a fan can provide, an alternative is available, in an evaporative cooling unit. These portable units can be purchased for half the price of a potable A/C unit. They are more efficient, however, in smaller rooms.