Minnesota Boiler License Practice Exam 2025 – All-in-One Guide to Passing with Confidence

To find the energy rate needed to evaporate 34.5 lb of water at 212 °F in one hour, it's essential to understand the concept of latent heat of vaporization. The latent heat of vaporization for water at 212 °F (which is the boiling point) is approximately 970 BTU per pound. This means that to convert 1 pound of water at this temperature into steam, 970 BTU of energy is required.

To calculate the total energy required to evaporate 34.5 lb of water, you multiply the weight of the water by the latent heat of vaporization:

Energy required = 34.5 lb × 970 BTU/lb = 33,465 BTU

To find the energy rate in BTU per hour, since we are evaporating all this water in one hour, the rate remains the same:

Energy rate = 33,465 BTU/h

When rounded to a reasonable estimate, this is approximately 33,475 BTU/h. This rate is important because it informs the necessary boiler capacity to effectively produce the required steam output without interruption. Hence, the provided choice of 33,475 BTU/h accurately reflects the energy needed for this process, making it