Minnesota Boiler License Practice Exam

What is the square footage of heating surface for a flue that is 4 inches in diameter and 20 feet in length?

1. 25 sq ft

2. 251.32 sq ft

3. 2513 sq ft

4. 20.93 sq ft

The correct answer is: 20.93 sq ft

To determine the square footage of the heating surface for a flue, you need to calculate the surface area of a cylinder. The formula for the surface area of a cylinder (without the ends) is given by: \[ \text{Surface Area} = 2 \pi r h \] Where: - \( r \) is the radius of the cylinder - \( h \) is the height (or length) of the cylinder First, we need to convert the diameter of the flue to radius, since the radius is half the diameter. In this case, the diameter is 4 inches, so the radius \( r \) is: \[ r = \frac{4 \text{ in}}{2} = 2 \text{ in} \] Next, we convert the radius from inches to feet because we want the final answer in square feet. There are 12 inches in a foot, so: \[ r = \frac{2 \text{ in}}{12} = \frac{1}{6} \text{ ft} \] The length of the flue \( h \) is already given as 20 feet. Now, we can substitute these values into the surface area formula: \