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NFPA 110 Generator Fuel Requirements – Complete Guide
NFPA 110 Reference

NFPA 110 Generator Fuel Requirements: Complete Guide

Most of the NFPA 110 generator fuel requirements exist to answer one question: will the generator still be running on day three of an outage? The standard does not care how powerful the engine is if the tank runs dry, the fuel has gone stale, or the supply was quietly borrowed for another purpose. This guide sets out what NFPA 110 requires for fuel storage, quality, and delivery, so your emergency power system passes inspection and, more importantly, works when it is called on.

Fuel Storage & Sizing
Day Tanks & Bulk Storage
Testing & Piping Rules
View the Full Guide
Free reference for engineers, facility managers, and specifiers.
Shandong Huali

Generator Sets & Fuel Systems

We manufacture diesel generator sets from 8 to 4,000 kVA and supply the base‑frame tanks, day tanks, and bulk storage systems that NFPA 110 fuel requirements are built around. We specify to NFPA 110 for our North American customers every day — this guide is drawn from that same experience.

8–4,000 kVA generator range
25+ Years experience
20+ Countries supplied
What Is NFPA 110? – Emergency Power Systems
NFPA 110 Reference

What Is NFPA 110?

NFPA 110, the Standard for Emergency and Standby Power Systems, governs how an Emergency Power Supply System (EPSS) is designed, installed, tested, and maintained. It classifies systems by Level and runtime Class, and it is those two designations that drive the fuel requirements.

Level 1 Life‑Safety Critical

A system whose failure could result in loss of human life or serious injury — hospitals, high‑rise life‑safety systems, and similar critical loads. Level 1 systems carry the strictest fuel provisions.

Level 2 Less Critical

Covers everything less critical than Level 1, where failure is inconvenient or costly but not life‑threatening. Fuel requirements are less stringent, but still governed by the standard.

Class Runtime Hours

The minimum time, in hours, that the system must run at its rated load without refueling. Common classes are 24, 48, 72, and 96 hours. Class 96 is typical for hospitals and Level 1 critical facilities.

Level + Class = Fuel Requirement

Your Class number is the first input to every fuel decision that follows. A Level 1, Class 96 system demands a different fuel storage solution than a Level 2, Class 24 system — and NFPA 110 sets the rules for both.

Key Takeaways

NFPA 110 at a Glance

01
NFPA 110 Governs EPSS

The standard for Emergency Power Supply Systems — design, installation, testing, and maintenance of backup power.

02
Level 1 = Life‑Safety

Systems where failure could cause loss of life or serious injury. Hospitals and high‑rise life‑safety systems are typical Level 1 applications.

03
Level 2 = Inconvenience

Less critical systems where failure is costly or inconvenient but not life‑threatening.

04
Class = Runtime Hours

24, 48, 72, or 96 hours of runtime at rated load without refueling. Class 96 is common for hospitals and other critical facilities.

Generator Fuel Tank Sizing Table – NFPA 110 Reference
NFPA 110 Fuel Sizing

Generator Fuel Tank Sizing Table

The values below are approximate, full‑load estimates using the industry average of roughly 0.07 gallons per kW per hour. Use them for planning; final sizing should reflect your actual expected load and fuel consumption.

Generator Fuel Tank Sizing — Full‑Load Estimates
Generator Rating (Standby) Full‑Load Consumption (gal/hr) Class 48 Tank Class 72 Tank Class 96 Tank
100 kW7450 gal670 gal900 gal
250 kW181,150 gal1,730 gal2,300 gal
500 kW352,240 gal3,360 gal4,470 gal
750 kW533,390 gal5,090 gal6,790 gal
1,000 kW704,480 gal6,720 gal8,940 gal
1,500 kW1056,720 gal10,080 gal13,410 gal
2,000 kW1408,960 gal13,440 gal17,870 gal
Based on ~0.07 gal/kW/hr — actual consumption varies by engine efficiency, load factor, and operating conditions.

Two Additional NFPA 110 Constraints

Diesel storage inside or on top of a structure is limited to 660 gallons (NFPA 110 7.9.5). Larger requirements need an outside or underground bulk tank with a day‑tank refueling system.

NFPA 110 7.9.1.3 requires the tank to be sized so fuel is consumed within its storage life, or you must provide for fuel polishing and remediation, because diesel degrades within 6 to 12 months in storage.

Key Takeaways

Sizing & Code Rules

01
0.07 gal/kW/hr Average

Industry average for diesel generator fuel consumption at full load. Actual consumption varies by engine efficiency and load factor.

02
660 gal Limit for Indoor Tanks

NFPA 110 7.9.5 caps diesel storage inside or on top of a structure at 660 gallons. Larger needs an outside or underground bulk tank.

03
Fuel Storage Life: 6–12 Months

Diesel degrades within 6 to 12 months. NFPA 110 7.9.1.3 requires the tank to be sized so fuel is consumed within its storage life, or you must provide fuel polishing.

04
Day‑Tank Systems

For systems requiring more than 660 gallons, a day‑tank refueling system from an outside bulk tank is the standard NFPA 110 solution.

How to Calculate Generator Fuel Tank Size
NFPA 110 Fuel Sizing

How to Calculate Generator Fuel Tank Size

Accurate sizing starts with real fuel consumption at your expected emergency load, not the nameplate rating. Diesel engines are less efficient at partial load, so the standard practice is to calculate against the load the generator will actually carry (typically 50% to 80% of capacity) rather than 100%.

STEP 01

Determine Your Class

48, 72, or 96 hours — from your facility's code requirements.

STEP 02

Establish Consumption

At the expected emergency load, in gallons or liters per hour.

STEP 03

Multiply

Class hours × consumption rate = required fuel volume.

STEP 04

Apply the 133% Buffer

Add a 33% reserve for the final bulk-tank volume per NFPA 110.

Full‑Load Tank Size Estimates — 133% Buffer Applied
Generator Rating Full Load (gal/hr) Class 48 Class 72 Class 96
100 kW7450 gal670 gal900 gal
250 kW181,150 gal1,730 gal2,300 gal
500 kW352,240 gal3,360 gal4,470 gal
750 kW533,390 gal5,090 gal6,790 gal
1,000 kW704,480 gal6,720 gal8,940 gal
1,500 kW1056,720 gal10,080 gal13,410 gal
2,000 kW1408,960 gal13,440 gal17,870 gal
Based on ~0.07 gal/kW/hr with 133% buffer applied. Actual consumption varies by engine efficiency, load factor, and operating conditions.
Key Takeaways

Sizing Rules

01
Use Expected Load, Not Nameplate

Diesel engines are less efficient at partial load. Size against the load the generator will actually carry (typically 50–80% of capacity).

02
Class × Consumption = Volume

Multiply your Class hours (48, 72, or 96) by the actual consumption rate at your expected load to get the required fuel volume.

03
Apply the 133% Buffer

NFPA 110 requires a 33% reserve above the calculated volume for the final bulk‑tank size. The table above has this applied.

04
Indoor Tank Limit: 660 Gallons

NFPA 110 7.9.5 caps indoor diesel storage at 660 gallons. Larger systems require outside or underground bulk tanks with day‑tank refueling.

NFPA 110 Compliant Emergency Generator Solutions
NFPA 110 Solutions

NFPA 110 Compliant Emergency Generator Solutions

An NFPA 110 compliant emergency generator is not a single engine on a frame. It is a complete emergency power supply system: the generator set, automatic transfer switch, controls, starting system, and fuel source, engineered to work together and tested as one unit before delivery.

01

Level 1, Type 10, Class-Tunable

We configure emergency standby generator sets to Level 1, Type 10 operation, restoring acceptable power within 10 seconds through an automatic transfer switch. The Class, and therefore the fuel system, is tuned to your project. Deep Sea, ComAp, and Cummins PowerCommand® controllers provide the automatic start, voltage and frequency regulation, and event logging that NFPA 110 Level 1 systems require.

02

Engine Options

Fuel efficiency drives the tank size, which is why engine choice matters. We integrate Cummins, Perkins, Weichai, and MTU engines paired with Stamford or Leroy Somer alternators. That flexibility lets you match fuel consumption to your Class requirement rather than over‑sizing the tank to compensate for an inefficient engine.

03

Sub‑Base vs. Bulk Tank Fuel Systems

For smaller installations, an integrated sub‑base tank keeps fuel storage compact and self‑contained. For larger Class 96 facilities, a day tank plus bulk tank configuration is the norm, feeding fuel automatically while keeping stored diesel within its usable life. We supply both, plus double‑wall tanks and fuel‑polishing provisions, so the fuel system is part of the engineered package, not an afterthought.

04

Hospitals & Healthcare: Class 96

Hospitals run on Level 1, Type 10 systems, and most plan for 96 hours of runtime to protect life‑safety systems, critical care equipment, and essential services. Our hospital backup power sets are configured with the fuel storage, redundancy (N+1 or N−1), and 2‑hour fire‑rated enclosure requirements that NFPA 110 and NFPA 99 demand.

05

Data Centers & Mission‑Critical Facilities

Data centers typically operate Level 1, Type 10 systems with runtime driven by business‑continuity goals and fuel capacity. Our data center backup generators are rated for sustained high‑load operation and modular scalability. Beyond healthcare and data centers, NFPA 110 governs emergency power for fire pumps, evacuation systems, and critical industrial processes — our standby power solutions span 8 kVA to 4,000 kVA, covering everything from a single fire pump to a full facility.

Every Shandong Huali NFPA 110 compliant system is engineered to the Level, Type, and Class your facility requires — not a generic standard.

NFPA 110 Applications – Hospitals, Data Centers & Industrial
NFPA 110 Applications

Applications

NFPA 110 compliance looks different in every facility. Here is how Level 1, Type 10 systems apply across the three most common use cases.

🏥 01

Hospitals & Healthcare

Hospitals run on Level 1, Type 10 systems, and most plan for 96 hours of runtime to protect life‑safety systems, critical care equipment, and essential services.

Our hospital backup power sets are configured with the fuel storage, redundancy (N+1 or N−1), and 2‑hour fire‑rated enclosure requirements that NFPA 110 and NFPA 99 demand.

Class 96
🖥️ 02

Data Centers

Data centers typically operate Level 1, Type 10 systems with runtime driven by business‑continuity goals and fuel capacity. Generators must handle rapid, dynamic load changes and preserve power quality under load.

Our data center backup generators are rated for sustained high‑load operation and modular scalability as the facility grows.

Class 24–72
🏭 03

Mission‑Critical & Industrial

Beyond healthcare and data centers, NFPA 110 governs emergency power for fire pumps, evacuation systems, and critical industrial processes where power loss carries serious risk.

Our standby power solutions span 8 kVA to 4,000 kVA, covering everything from a single fire pump to a full facility.

Custom Class

Every application has its own Level, Type, and Class requirements. Shandong Huali configures each system to the specific code and operational demands of your facility — not a one‑size‑fits‑all solution.

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Why Shandong Huali

More than 100 CNC machines and a national-standard testing center give us full control over quality from engine to enclosure.

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