This is not a valid question. Btu is a quantity of thermal energy, 300 degrees is a temperature, not a quantity of energy
There are 100,000 BTU (British Thermal Units) in a therm.
There are approximately 0.00094781712 BTU in one joule.
1 Therm is equal to 100,000 BTU.
There are 0.00001 therms in 1 BTU.
There are approximately 20,472 BTU in 6 kW.