BTU Meters are widely used in the central air-conditioned systems using chilled water systems, for measuring the thermal energy produced or consumed. BTU is British Thermal Unit (British thermal unit). 1 BTU is the energy required to heat 1 pound of water to 1 degree Fahrenheit, 1 BTU is about 1055 joules. Putting it together with the hour, it means how many British thermal units of heat can be pumped out by the air conditioner per hour using the heat pump principle. According to 1BTU=1055.05585 joules, you can calculate how many joules of heat the air conditioner can pump per hour.