An air conditioner's BTU rating is a clear indication of its cooling power. When choosing between a 5,200 BTU and a 6,000 BTU air conditioner, you need to take into consideration the size of the room and other factors that may contribute to its cooling needs.
British Thermal Units
BTU is the common abbreviation for British thermal unit. This is the unit of measurement used to rate the cooling power of air conditioners. One BTU is the amount of heat it takes to warm a pint of water by one degree Fahrenheit. An air conditioner's rating reflects the amount of heat it can extract from the air each hour; for example, a 6,000 BTU air conditioner could theoretically reduce the temperature of 100 more gallons of water by one degree than could a 5,200 BTU air conditioner.
Getting the Right Size
When choosing between a 5,200 and a 6,000 BTU air conditioner, don't always default to the larger model. While an air conditioner that's too small will have difficulty cooling a room on warm days, an air conditioner that's too powerful will not only waste energy but will short-cycle, cooling your room rapidly but then shutting off before a significant amount of humidity is removed, thus leaving the air damp. The minimal difference between the two sizes makes this a negligible problem, but it becomes important with greater variation in BTU ratings.
5,200 BTU Air Conditioner
According to the U.S. Department of Energy, a 5,200 BTU air conditioner is best suited for rooms of 100 to 150 square feet, with those near the upper end of that range being ideal. This size is perfect for cooling sunny rooms that fall within the lower end of the range, and though less ideal, can handle slightly larger sunlit rooms as well.
6,000 BTU Air Conditioner
A 6,000 BTU air conditioner is ideal for a room of 200 square feet, and is fine for those with a square footage smaller than or in excess of that by 50 feet or so. This air conditioner is also best for rooms normally of a 5,200 BTU size that are regularly frequented by at least three people, with the greater cooling power counteracting the higher levels of body heat.