🔋 Required Battery Capacity
Sizing Breakdown
Full Calculation Table
| Fixture Group | Watts Each | Subtotal |
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How to Use the Emergency Lighting Calculator
Standard egress paths need 30 minutes of runtime at 10 lux average. High-rise buildings and certain Group B occupancies need 2 hours. Generator and fire pump rooms need 2 hours at a higher 50 lux average. Use Custom if your specific occupancy classification calls for different values.
Enter the wattage and quantity for each type of emergency fixture or remote head on the circuit.
Most unit equipment runs on 6, 12, or 24 VDC battery packs. The aging derate builds in a safety margin so the system still meets runtime requirements near the end of the battery's service life.
The calculator totals connected fixture load and works out the required battery capacity in amp-hours to meet the selected runtime with the aging derate applied.
Sizing Emergency Lighting for Mechanical Rooms
Emergency lighting exists to get people out safely when the regular power supply fails, and that includes mechanical and equipment rooms where HVAC technicians often work alone in tight spaces. The National Building Code of Canada sets specific illumination and runtime requirements that depend on the space type and the building's overall occupancy classification.
Illumination Requirements
For most egress paths, corridors, and exit routes, the NBC requires an average illumination of at least 10 lux at floor or tread level, with no point falling below 1 lux. Generator rooms and fire pump rooms carry a higher requirement of 50 lux average, reflecting the importance of being able to see clearly while operating critical emergency equipment during a power failure. These illumination levels need to be verified with a photometric layout from the fixture manufacturer's data, not assumed from wattage alone, since beam spread and mounting height both affect actual lux at floor level.
Runtime Requirements
The baseline runtime requirement under the NBC is 30 minutes, but this extends depending on the building. Buildings within the scope of high-rise provisions, and certain Group B occupancies like care facilities, need 1 to 2 hours of emergency lighting runtime. Generator rooms and fire pump rooms also carry a 2-hour requirement, since these spaces house equipment that may need extended attention during an emergency. Always confirm the exact runtime that applies to your specific building and space type against the current code edition adopted in your province, since requirements can vary by building height, occupancy, and local amendments.
Battery Capacity and Aging
Battery capacity fades over the service life of the unit, which is why this calculator includes an aging derate, typically 20% to 25%, on top of the calculated runtime requirement. Sizing the battery without this margin risks the system falling short of its required runtime once the battery has aged a few years into its service life, right when a real emergency is most likely to reveal the shortfall.
Connecting to the Branch Circuit
Emergency lighting circuits need their own dedicated breaker that serves no other equipment, and that breaker must connect to an emergency power supply as required by the applicable code. If you're sizing a panel that includes emergency lighting circuits alongside regular HVAC loads, the electrical load schedule tool helps keep these circuits clearly separated and documented.
Next Steps
Once battery capacity is confirmed, check the wire size calculator for the emergency circuit conductors, and the breaker size calculator to confirm the dedicated breaker is correctly sized for the connected fixture load.
Frequently Asked Questions
The National Building Code of Canada requires emergency lighting on egress paths to maintain an average illumination of at least 10 lux at floor or tread level, with a minimum value of not less than 1 lux at any point. Generator rooms and fire pump rooms have a higher requirement of 50 lux average. Always confirm the exact requirement for your specific space type and occupancy classification against the current code edition adopted in your province.
The National Building Code sets a minimum runtime of 30 minutes for most occupancies, but this extends to 1 hour for certain Group B occupancies and 2 hours for buildings within the scope of high-rise provisions, along with generator and fire pump rooms. The exact runtime depends on the building's height, major occupancy classification, and specific space type, so always confirm the applicable runtime before sizing battery backup equipment.
Battery capacity declines gradually over its service life, so a battery sized to exactly meet the runtime requirement on day one may fall short after a few years of use. Applying a 20% to 25% derate when sizing the battery builds in a safety margin so the system still meets its required runtime even as the battery ages, which matters most during an actual emergency rather than during a routine test.
No. Emergency lighting circuits need a dedicated breaker that serves no other equipment, and that breaker must be connected to an emergency power supply as required by the applicable building code. Mixing emergency and regular lighting on the same circuit defeats the purpose of having a separate emergency power source. The electrical load schedule tool can help keep these circuits clearly documented and separated on the panel schedule.