On a smooth ceiling with a listed spacing of 50 feet, and a ceiling height of 10 feet above finished floor, the spacing between heat detectors should be ____ feet?

• A. 40
• B. 35
• C. 50
• D. 45

Answer: (C)

When heat detectors are mounted on a smooth ceiling, the spacing is defined by the detector’s listing. The listed spacing is the maximum distance allowed between detectors along the ceiling to ensure the area is protected. The ceiling height of 10 feet does not change this requirement for a smooth ceiling—the listing already assumes typical room geometry. Therefore, detectors should be placed no more than 50 feet apart. Using smaller spacings (like 40, 35, or 45 feet) isn’t required by the listing and would simply be more conservative than necessary in this setup.