Fire Alarm Coverage Calculator

Under NFPA 72 (National Fire Alarm and Signaling Code), spot-type smoke detector listed spacing is not reduced for ceiling height -- it holds at the standard 900 sq ft coverage across this calculator's full ceiling-height range. The ceiling-height spacing-reduction table in NFPA 72 -- Table 17.6.3.5.1, "Heat Detector Spacing Reduction Based on Ceiling Height" -- applies specifically to heat detectors, which is why Ceiling Height only affects the result when Detector Type is set to Heat Detector.

Smoke detectors are listed for 900 sq ft of coverage under standard NFPA 72 smooth-ceiling spacing, while heat detectors are listed for a larger 2,500 sq ft. Heat detectors respond to a slower, more localized rise in temperature rather than to smoke that can spread and be sensed across a wider area, so they're typically spaced farther apart and used in environments where smoke detection isn't practical.

Only for heat detectors. NFPA 72 cuts heat detector spacing to two-thirds at right angles to beams projecting more than 4 in. below the ceiling, and this calculator applies that to the Heat Detector option. Spot-type smoke detectors have no equivalent percentage reduction -- on a sloped or peaked ceiling the standard spaces them on the ceiling's horizontal projection and adds one detector near the peak, and on a beamed ceiling the criteria are relative to ceiling height. Use the Smoke Detector Spacing calculator for that geometry.

Not exactly -- Detectors Required is Room Area divided by Coverage per Detector, rounded up to a whole number, so it always increases (or stays the same) as Room Area grows, but the rounding means it doesn't scale as a perfectly smooth multiple. It will never decrease when Room Area increases with everything else held fixed.