Fire Alarm Battery Calculator

Enter standby and alarm current draws. This tool computes the total amp-hours needed per NFPA 72 §10.6.7, applies the required 20% derating, and rounds up to the next commercially available battery size.

Educational estimator. Not a substitute for a licensed design. Battery sizing must be signed by a qualified fire-alarm designer (NICET II or higher) or a PE. Cite: NFPA 72-2022 §10.6.7.

Standby load (mA) Total non-alarm current draw from the FACP: control panel + supervised devices + comm gateway. Sum from device data sheets or the panel's standby-current worksheet.

Standby hours required Local commercial fire alarm is 24 hours. Central-station/proprietary supervising is 60 hours. Smoke-control-only is 12.

Alarm load (mA) Peak alarm-mode draw: NAC circuits (horns, strobes, speakers), releasing outputs, panel alarm current. Read from the NAC amperage worksheet + panel spec sheet.

Alarm minutes required Standard fire alarm: 5 minutes. Voice / mass notification / high-rise emergency comms: 15–30 minutes depending on the classification.

Aging factor (%) NFPA 72 §10.6.7.2.1 requires 20% derating (baked in below). Some designers add another 10–15% for battery aging and temperature. Add here only if your jurisdiction or spec demands it. Leave at 0 for a strict code-minimum calc.

Fire Alarm Battery Calculator

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