12,000 BTU Portable Air Conditioners are the most commonly sold size and style of this type of cooling unit. Given that the standard length of lumber in the United States starts at eight feet, the average room that needs to be cooled requires about the same cubic feet to be cooled. At 12,000 BTUs, there is enough power for the portable air conditioner to run with horsepower to spare.

When we speak of power ratings, we speak of BTUs or "British Thermal Units". This is the energy required to raise the temperature of one pound of water by one degree fahrenheit. This is about the same energy contained in a single paper match or the energy required to raise one pound to a height of 778 feet in the air.

A 12000 BTU portable air conditioner is rated to cool a room between 450 and 550 square feet, or a square room 22 feet on a side. Which sounds like too much, but one does not want the unit to be working at its maximum capacity.

Why so many portable air conditioners that work at 12,000 BTUs? It has to do with standardization within the industry. In the United States, cooling units were rated in "tons", which was the energy required to melt a ton (2,000 pounds) of ice in a 24 hour period. A single ton of cooling just happens to be 12,000 BTU, the easiest and most measureable unit. Making a unit at this rating is quicker and cheaper to certify at the governments ratings boards.

A 12000 BTU portable air conditioner is pound-for-pound and ton-for-ton your best and largest ac for the dollar on the market today.