Emergency Generator Size Calculator
Calculate the appropriate emergency generator size for your backup power needs. Enter your critical power requirements below.
Essential Loads
Optional Loads
Emergency Settings
List of the Top 10 Best Emergency Generators:
How to Size an Emergency Generator?
Understanding Emergency Power Requirements
Properly sizing an emergency generator requires careful consideration of critical loads and backup scenarios:
- Load Classification:
- Essential Loads: Critical systems that must remain operational (e.g., life safety, medical equipment)
- Optional Loads: Non-critical systems that can be powered if capacity allows
- Starting Surge: Temporary power requirements during equipment startup
- Runtime Requirements:
- Determine how long you need backup power (typically 8-72 hours)
- Longer runtimes require larger fuel storage
- Consider fuel availability during emergencies
Common Emergency Applications
| Application Type | Typical Essential Loads | Recommended Size Range |
|---|---|---|
| Residential | Refrigeration, Sump Pump, Basic Lighting | 5-20 kW |
| Healthcare | Life Support, Medical Equipment, Emergency Lighting | 50-500 kW |
| Commercial | Security Systems, Emergency Lighting, Elevators | 20-200 kW |
| Data Centers | Servers, Cooling Systems, UPS | 100-2000 kW |
Common Emergency Equipment Power Requirements
| Equipment Type | Running Power (kW) | Starting Power (kW) |
|---|---|---|
| Residential Refrigerator | 0.7 | 2.2 |
| Sump Pump (1/2 HP) | 0.4 | 1.2 |
| Medical Ventilator | 0.3 | 0.5 |
| Emergency Lighting (per fixture) | 0.02 | 0.02 |
Important Emergency Sizing Considerations
1. Critical Load Prioritization
Identify what must remain powered during an outage:
- Life safety systems (fire alarms, emergency lighting)
- Medical equipment (hospitals, nursing homes)
- Building infrastructure (elevators, sump pumps)
- Communication systems
2. Fuel Considerations
Emergency generators require reliable fuel sources:
- Diesel: Most common, requires on-site storage
- Natural Gas: Continuous supply but may fail during disasters
- Propane: Clean-burning alternative with long shelf life
- Consider dual-fuel capability for critical applications
3. Regulatory Requirements
Emergency generators must comply with:
- NFPA 110 (Standard for Emergency and Standby Power Systems)
- Local building codes
- EPA emissions regulations
- Life safety requirements (hospitals, high-rises)
Frequently Asked Questions
What's the difference between emergency and standby generators?
Emergency generators are for life safety systems and must start within 10 seconds per NFPA 110. Standby generators are for convenience and typically start within 30-60 seconds. Emergency systems have stricter maintenance and testing requirements.
How often should I test my emergency generator?
NFPA 110 requires monthly testing under load for at least 30 minutes, plus annual 4-hour tests. Always follow manufacturer recommendations and local regulations for your specific application.
How much fuel storage do I need for emergency power?
Most codes require at least 8 hours of fuel at full load. Critical facilities often require 24-72 hours. Calculate based on your generator's consumption rate at expected load and required runtime.
Should I size for all loads or just essential loads?
Size for essential loads first, then consider optional loads if budget allows. For critical facilities, include all life safety and legally required loads plus a safety margin of 10-25%.
How do I account for generator efficiency?
Most generators operate at 80-90% efficiency under optimal load. Oversizing can reduce efficiency. Our calculator includes typical efficiency factors in its recommendations.
What maintenance does an emergency generator require?
Regular maintenance includes oil/filter changes, coolant checks, battery testing, and load bank testing. Follow manufacturer schedules and document all maintenance for compliance purposes.