BTU, or the British Thermal Unit, is the amount of heat required to raise one pound of water one degree Fahrenheit. The British Thermal Unit measures the amount of heat, or thermal energy. Temperature is the level rather than amount of heat. Therefore, there is no formula to convert a British Thermal Unit to Fahrenheit. Instead, the British Thermal Unit indicates the ability of a stove, heating system, grill, water heater and other appliances to increase temperature.
Find the British Thermal Unit rating for the appliance or equipment. Consult the specifications page of the owner's or operator's manual or the appliance's manual.
Determine the amount of space or water to be heated. Calculate the space in cubic feet by measuring the length, width and distance from floor to ceiling of the building or space to be heated and multiplying the three figures. For water, multiply the number of gallons to be heated or used by 8.3453, since one gallon of water equals 8.3453 pounds.
Multiply the cubic feet of the area to be heated by 0.133. Divide the British Terminal Unit of the heating unit by the factor of cubic feet and 0.133 to obtain the change in temperature. For heating water, divide the British Thermal Unit by the pounds of water to be heated.