Section 17.7.3/Heat Detector Spacing
NFPA 72 Section 17.7.3 covers heat detector spacing based on listed spacing, ceiling height reduction factors, and non-standard conditions.
Heat detectors must be spaced based on their listed spacing, which is determined by the manufacturer's listing. The installed spacing must not exceed the listed spacing. On smooth ceilings 10 feet or less in height, the listed spacing may be used without reduction. For ceilings higher than 10 feet, the spacing must be reduced per Table 17.6.3.5.1 based on ceiling height. Detectors must not be more than half the listed spacing from any wall.
Why this section exists
Heat detectors respond to the temperature rise from a fire. Unlike smoke, which rises and spreads quickly along the ceiling, heat dissipates more rapidly and takes longer to travel. The spacing requirements ensure that a fire between detectors produces enough heat at the ceiling to activate at least one detector before the fire grows to a dangerous size. Higher ceilings require closer spacing because heat dissipates more before reaching the ceiling.
What plan reviewers look for
Plan reviewers verify the listed spacing of the specified heat detector model and check the installed spacing on the floor plan. They apply the ceiling height reduction factor from Table 17.6.3.5.1 for spaces with ceilings above 10 feet. They verify that detectors are not more than half the listed spacing from walls.
Common violations
Related NFPA 72 requirements
Section 17.5.3 covers smoke detector spacing. Table 17.6.3.5.1 provides the ceiling height reduction factors. Section 17.7.5 covers heat detector spacing on peaked and sloped ceilings.