Spot Smoke / Heat Detector Count (Smooth Ceiling)

rows = ceil(length / listed spacing); columns = ceil(width / spacing); detectors = rows x columns; the first detector sits within spacing/2 of each wall. A 60 x 40 ft room at a 30 ft listed spacing takes 4 detectors (a 2 x 2 grid, 15 ft off each wall); a 100 x 80 ft open area takes 12. The 0.7-times-spacing rule confirms every point is covered; beams, high ceilings, and HVAC tighten it. An install estimate; the stamped fire-alarm plan and the AHJ govern.

rows = ceil(room_length_ft / listed_spacing_ft); cols = ceil(room_width_ft / listed_spacing_ft); detectors = rows x cols; wall_max_ft = listed_spacing_ft / 2.

NFPA 72 spot-detector grid identity by name (grid count over the listed spacing; wall maximum at half the spacing); first-principles grid arithmetic.

The grid arithmetic is public first-principles; the listed spacing comes from the device listing and the reductions from NFPA 72.

Estimate. AHJ and licensed professional govern.

Field names used by the API: room_length_ft, room_width_ft, listed_spacing_ft, detectors, wall_max_ft

• Listed spacing ~30 ft for spot smoke on a smooth ceiling; the device listing governsdevice listing / NFPA 72
• Coverage 0.7 x spacing to the farthest point; first detector within spacing/2 of each wallNFPA 72