Originally Posted by Stu Jackson
Stu, you are completely correct in noting the correct use of the term.
That said, I have been an HVAC engineer
for the past 45 years and commonly BTU/hour (BTU PER hour) is commonly used as a shorthand
A BTU/hour is 0.2930 watts or 0.0003929 horsepower, a measure of power. Power is the rate at which work is done or the heat rate hence the unit of time in the denominator.
A BTU is a measure of energy, work, heat. A BTU is 1055 joules. Work is the total change in kinetic energy.
What does this have to do with boiling water one might ask. The total amount of heat transferred to the water to make it boil is X BTU's.
The instantaneous rate at which the heat is transferred to the water, Y BTU/hr, is variable depending on the heat transfer equations. The equations account for the increasing water temperature at each instant in time due to the convection and radiation transfer of heat to the pot.
The burner rating is the rate at which the heat can be supplied or generated at an instant in time, BTU/hr. Bigger burner or hotter flame the BTU's/hr are greater.
At an instant in time only part of burner heat goes to actually heating
the water in the pot. The remainder heats the metal parts
, air, and via radiation, the surrounding environment
(think thermal light bulb shaped like the burner.)
Power, BTU's per unit time is the rate at which heat, BTU's, are supplied by the burner.