So the main question is what does BTU mean? Btu â British Thermal Unit (Btu) is the international measure of energy. A Btu is the amount of heat needed to raise 1 (one) pound of water by 1(one) degree Fahrenheit. In HVAC industry, Btu's measure the quantity of heat a conditioning unit can remove from a room per hours. One BTU per hour is equal to 0293 watts. As the Btu rating increases, so does the weight, size and cost of the air conditioner. To calculate how many BTUâs you need you can use this table.