Massachusetts Construction Supervisor License (CSL) Practice Test

What is the minimum required flue size for a rectangular chimney serving a fireplace with an opening of 500 square inches and a height of 15 feet?

1. 6 x 10

2. 8 x 10

3. 8 x 12

4. 10 x 12

The correct answer is: 8 x 12

To determine the minimum required flue size for a rectangular chimney serving a fireplace, you need to consider both the area of the fireplace opening and the height of the chimney. The general rule of thumb for sizing a chimney flue for a fireplace is to ensure that the flue area is at least 1/10 of the fireplace's opening area. In this case, the fireplace opening has an area of 500 square inches. Applying the guideline, the minimum flue area should be: 500 square inches / 10 = 50 square inches. The flue size options must then be evaluated to find one that meets or exceeds this size. For option C, which is an 8 x 12 rectangular flue: - Calculation: 8 inches x 12 inches = 96 square inches. This flue measures 96 square inches, which is significantly larger than the required 50 square inches. This makes it a suitable choice as it provides adequate draft and ventilation for the fireplace. In contrast, the other flue size options do not meet the criteria for adequate sizing or potentially could be below the required area, which may lead to inefficiencies in draft or combustion within the fireplace. Thus, the chosen size ensures compliance with building code