Heat Detector Spacing and Listed Spacing Adjustment
Heat detectors go where smoke detectors cannot survive or would false-alarm — kitchens, boiler rooms, parking. Their spacing is tighter and drops sharply with ceiling height.
Listed spacing
Heat detectors are listed for spacings such as 15 × 15 ft (4.6 m), 25 × 25 ft (7.6 m), or 50 × 50 ft (15 m) depending on the model. The listed value assumes a ceiling height of 3.0 m (10 ft) or less.
Ceiling-height reduction
Because a heat plume spreads and cools as it rises, NFPA 72 requires the spacing to be reduced for higher ceilings:
| Ceiling height | % of listed spacing |
|---|---|
| 0–3.0 m | 100% |
| 3.0–3.7 m | 91% |
| 3.7–4.6 m | 84% |
| 4.6–5.5 m | 77% |
| 5.5–6.7 m | 71% |
| > 6.7–9.1 m | ~63% and downward |
Rate-of-rise vs fixed temperature
- Rate-of-rise + fixed (combination) — general use; responds to a fast temperature climb and to a slow one reaching the set point.
- Fixed temperature only — where normal ambient swings are large or rapid (near ovens, outdoors), to avoid false alarms. Set point above the maximum expected ambient (e.g. 90 °C near kitchens).
Where heat detection is required or preferred
Kitchens and cooking areas, mechanical and boiler rooms, laundries, parking garages, attics and concealed spaces, and any environment too dirty, humid, or fume-laden for reliable smoke detection.
EngEst Pro’s FDAS Calculator applies the ceiling-height reduction to heat detector spacing for each room, selects rate-of-rise or fixed-temperature by room type, and lists the detectors in the BOM.
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