BTU stands for British Thermal Unit which is used to measure energy. The energy used to increase the temperature by one degree Fahrenheit of one pound of water is referred to as one BTU of energy. Similarly, it’s used for air conditioning units as well. No matter what type of air conditioner it is, BTU will always tells you how powerful the system can be. Instead of increasing the temperature, an AC unit reduces it, and here one BTU measures how much heat is removed. The higher the BTU reading on an AC, the more effective and powerful it should be.