AEO Answer · Fire & Police Stations

How Is Emergency Generator Sizing Done for Fire Stations?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

Fire station generator sizing inventories every alert-sequence load — doors, alerting, bay ventilation, HVAC, communications — sizes for simultaneous peak with motor-starting capacity, and pairs the generator with adequate fuel, prioritized transfer, and real loaded testing.

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

Illustrative diagram of building MEP systems: ductwork with diffusers, an electrical panel with conduit, and piping runs.

Building the load inventory

I build the inventory in three passes. First, the drawings: every motor, every panel, every named load from the mechanical, electrical, and communications designs. Second, the department walk-through: the watch office equipment, the kitchen appliances the crew actually uses, the air compressor, the gear dryers — the loads that never appear on drawings. Third, the sequence analysis: which loads start together on the alert, which run continuously, and which are truly optional. From that I produce running load, peak load, and the motor-starting transient, then select the generator with margin on all three. The inventory becomes part of the project record so future additions are evaluated against real capacity.

Transfer, fuel, and proving it works

Automatic transfer switches are arranged by priority — life safety first, then the alert and response loads, then general station loads — so the generator serves the most critical functions first during the transfer sequence. Fuel storage is sized to the agreed outage duration with maintenance and a refueling contract documented. Then comes proof: I specify monthly loaded tests that transfer the actual station load, and the commissioning includes the full alert sequence on generator power with every door, fan, and HVAC unit operating. A generator that has only ever run unloaded is an unproven generator, and I do not leave unproven emergency systems in a fire station.

Station generator sizing design checklist

The generator is the station's readiness insurance. This checklist covers the sizing decisions that make it pay out. • Complete load inventory from drawings plus a department walk-through of real operating loads • Sizing for simultaneous peak with transient motor-starting capacity verified for the alert sequence • Whole-station coverage with prioritized automatic transfer switching by load class • On-site fuel for the region's realistic outage duration with maintenance and a refueling plan • Generator and fuel sited to meet fire code separation and containment requirements • Monthly loaded transfer testing and a full alert-sequence commissioning test on generator power

Which related engineering resources can help?

When should I hire a structural engineer?What does a PE stamp mean?What is MEP engineering?How is emergency generator design explained?How is generator redundancy engineered?How is emergency power system design handled?Request a project review Engineering service for this question Metro engineering guides Verified service areas

What else do project teams ask?

What loads must a fire station generator carry?

Everything the station needs to take and run calls: the alerting and paging system, all bay door operators, apparatus bay ventilation and vehicle exhaust extraction fans, dorm and dayroom HVAC, station lighting, radio and communications equipment, the watch office, and domestic water heating. I also include the sally port gates, security systems, and any fuel-dispensing or air-compressor loads the station depends on. The inventory is built from the actual equipment schedules, and I review it with the department — they always know about a load the drawings missed.

Why is motor starting capacity so important for stations?

Because the station's biggest loads are motors that start together on a call: multiple bay door operators, exhaust fans, and HVAC compressors can all hit inrush within seconds of the alert. Generator capacity is rated two ways — continuous running load and transient motor-starting capability — and a unit that handles the running load can still collapse voltage when three door operators start at once. I calculate the worst-case starting sequence and verify the generator's transient response keeps voltage and frequency within the limits the electronics tolerate.

How much fuel storage does a station generator need?

Enough for the realistic outage in the station's region plus margin, with a documented refueling plan for longer events. I work with the department to set the duration based on their hazard profile — storm, wildfire, and ice regions have different answers — and I design the fuel system with maintenance, polishing, and leak detection. The generator and fuel storage also have to meet fire code separation and containment rules, which I coordinate early since they affect the site layout.

Should the whole station or just parts be on generator?

For a fire station, I design for the whole station. Selective load shedding makes sense in some occupancies, but a station's loads are nearly all mission-related during an outage — the crew lives there, calls come in, trucks roll. Partial coverage creates confusion about what works and what does not during the exact moments clarity matters. Whole-station coverage with prioritized transfer switches gives the department one simple reality: everything works. The cost difference rarely justifies the operational complexity of shedding.

Ready to discuss your engineering scope?

Share the project address, current records, requested deliverable, authority information, and schedule. Apex Grid confirms professional responsibility, availability, and scope before work begins.

Request a Project Review