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Notification Appliance Calculator (Horns + Strobes)

An audibility test that comes up 4 dBA short in the back office, a 15 cd strobe in a room that needed 30, a 240-foot corridor with two strobes instead of four — these are the acceptance-test failures that turn a one-day final into a return trip. This tool applies NFPA 72-2022 Chapter 18: public-mode and private-mode audibility, the 110 dBA ceiling, wall and ceiling strobe tables by room size, the corridor rule, and sleeping-room requirements.

Educational estimator, not a sealed design. Notification appliance selection is part of the fire alarm design of record and is proven by the acceptance test — a sound level meter at 5 ft above the floor and a walk of every room with the strobes flashing. Sound level at distance is a free-field inverse-square estimate; real rooms add reflections and doors. Strobe tables are NFPA 72-2022 Table 18.5.5.7.1(a) and (b) as published. Texas jurisdictions adopt different editions and local amendments govern — confirm with your AHJ.

1. Audible: will the horn be loud enough where people are?

NFPA 72-2022 §18.4.4.1 (public mode): at least 15 dBA above the average ambient sound level, or 5 dBA above the maximum sound level lasting at least 60 seconds, whichever is greater, measured 5 ft above the floor. Private mode (§18.4.5.1) is 10 dBA / 5 dBA. Sleeping areas (§18.4.6.1) need at least 75 dBA at the pillow. Horn ratings are published at 10 ft; sound falls off 6 dB for every doubling of distance.

Annex A values are typical, not requirements. A measured ambient (sound level meter, normal operating conditions) always beats a preset.
Equipment that runs for a minute or longer: compressors, dust collectors, dish machines. Leave blank if nothing sustained exceeds the average.
UL 464 ratings are reported at 10 ft. Use the rating for the tap and voltage actually set, and the reverberant-room value if the sheet lists both.
NFPA 72 does not publish a door-loss value. Enter what your meter readings on similar doors show; leave blank for a direct line of sight.
Minimum hearing distance. The combined level of ambient plus all appliances must not exceed 110 dBA there (§18.4).

2. Visible: strobe candela for a room

NFPA 72-2022 Table 18.5.5.7.1(a) sets the minimum effective intensity for a wall-mounted strobe by the size of the square room it sits in; Table 18.5.5.7.1(b) does the same for ceiling-mounted strobes by lens height. Non-square or off-center rooms use the farthest wall or twice the distance to the farthest adjacent wall, whichever is greater (§18.5.5.7).

Along the wall the strobe is mounted on, measure to the far corner. §18.5.5.7 doubles this distance when it exceeds the room's long dimension.
§18.5.5.1: the entire lens between 80 in. and 96 in. above the floor. If the ceiling forces it lower, mount within 6 in. of the ceiling and the room size is reduced by twice the shortfall below 80 in.
Table 18.5.5.7.1(b) has rows for lens heights up to 10 ft, 20 ft, and 30 ft. Above 30 ft, §18.5.5.7 requires suspending the appliance to 30 ft or less or using a performance-based alternative.

3. Visible: corridor strobes

NFPA 72-2022 §18.5.5.8: in corridors 20 ft wide or less, strobes of at least 15 cd are located not more than 15 ft from each end and not more than 100 ft apart. Corridors wider than 20 ft use the room tables in Panel 2. Fire doors, elevation changes, and other interruptions to the view path start a new corridor.

Measure from end wall to end wall, or to a fire door or a turn that breaks the line of sight (§18.5.5.8).

4. Sleeping room: strobe and sounder at the pillow

NFPA 72-2022 §18.5.5.10: a sleeping-area strobe within 16 ft of the pillow must be at least 110 cd if the lens is 24 in. or more below the ceiling, or 177 cd if it is less than 24 in. below the ceiling. §18.4.6: the audible signal must reach 75 dBA at the pillow and, where required to wake occupants, use the low-frequency 520 Hz square-wave signal.

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Public vs private mode, why horns are rated at 10 ft, how the strobe tables work for odd-shaped rooms, corridors, sleeping rooms, and 520 Hz.

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