Generator Fuel Options Reference

Overview

The fuel decision determines cost per kWh, run duration, refueling logistics, + storage hazards. For standby generators, fuel choice is typically natural gas or propane; for portable, also gasoline or diesel. This reference covers trade-offs.

Natural gas (most common standby)

Pros

• Continuous supply (utility pipeline; no refueling)
• Lower cost per BTU than propane
• Indefinite runtime
• No fuel storage on-site
• No fuel spills
• No fuel theft

Cons

• Subject to utility outage (rare, but earthquakes, gas line damage)
• Requires gas pipeline at property
• Slightly lower power density than gasoline/diesel
• Pressure drop concerns with high gas demand (verify meter sizing)

Best for:

• Suburban homes connected to natural gas
• Permanent installations
• Customers wanting "set it and forget it"

Cost (2025):

• Natural gas: (100,000 BTU)
• Generator at full load: ~ of run time

Propane (second most common standby)

Pros

• Higher power density than natural gas
• Can be stored on-site (no utility dependency)
• Works in rural areas
• Cleaner burn than gasoline/diesel
• Long shelf life (no degradation like gasoline)

Cons

• Tank required (storage + space)
• Refilling costs + scheduling
• Tank monitoring required
• Vapor pressure drops in extreme cold (under -10°F gradually)
• Initial tank cost

Best for:

• Rural / no natural gas service
• Customers wanting fuel independence

Tank sizing:

For a typical home + 22kW generator: 500-gallon tank gives roughly 1 week of runtime. Adjust for actual load + outage duration concerns.

Cost (2025):

• Propane:
• Generator at full load: ~
• Annual filling cost (if used):

Gasoline (portable generators)

Pros

• Widely available (any gas station)
• Cheap fuel
• Easy to handle small quantities

Cons

• Limited shelf life (3-6 months without stabilizer; 1-2 years with)
• Flammable + explosive risk
• Theft concern
• Refueling required during outage
• Carburetor gumming if not maintained

Best for:

• Portable generators
• Short-duration outages
• Customers who can refuel during outage

Storage:

• Approved fuel cans (5 gallon max)
• Vented, cool location
• Away from ignition sources
• Fresh fuel only (stabilizer recommended)
• Code limits typical: 25 gallons in residential garage; varies by jurisdiction

Cost (2025):

• Gasoline:
• 5kW portable at full load: ~

Diesel (commercial + large residential)

Pros

• Highest energy density (longest runtime per gallon)
• Long fuel storage life (with treatment)
• Reliable in cold weather
• Heavy-duty engine (longer lifespan)

Cons

• Most expensive fuel
• Smelly + noisy operation
• Particulate emissions higher
• Diesel engines more expensive to maintain
• Less common in residential

Best for:

• Large estates
• Mission-critical applications (medical equipment, server rooms)
• Locations without natural gas + budget for premium

Cost (2025):

• Diesel:
• Large generator (50kW) full load: ~

Dual-fuel options

Some generators accept multiple fuels:

• Tri-fuel (gas, propane, natural gas): portable + commercial
• Dual-fuel (gasoline + propane): common portable upgrade
• Convertible: natural gas + propane (standby with conversion kit)

Pros:

• Fuel flexibility
• Backup option if primary unavailable

Cons:

• More complex carburetion
• Slightly more expensive
• Different output ratings per fuel type

Fuel pressure requirements (gaseous)

Natural gas:

• Most generators: 7-11 inches water column (low pressure)
• Some commercial: 1-2 PSI
• Generator manufacturer specifies; check supply pressure

Propane:

• 11-14 inches water column (slightly higher than natural gas)
• Regulator at tank provides correct pressure

Important: if pressure too low, generator runs lean (worse emissions, won't hit full power); too high, generator runs rich (carbon buildup, fouled spark plugs).

Fuel line sizing

For natural gas runs:

• 1/2" pipe: ≤ 5 ft, up to 14 kW
• 3/4" pipe: ≤ 25 ft, up to 22 kW
• 1" pipe: ≤ 50 ft, up to 30 kW
• 1-1/4" pipe: longer runs or larger generators

For propane: similar but verify with manufacturer specs.

Plumber should verify pressure at generator under full-load conditions.

Code + regulatory

Local codes:

• NFPA 54 (Natural Gas Code)
• NFPA 58 (Liquefied Petroleum Gas Code)
• IFGC (International Fuel Gas Code)
• Local amendments

Permits: gas permit + electrical permit + sometimes building permit

Inspection: pressure test + leak check + permit closeout

Tank placement (propane)

Code-required distances:

• 10 ft from home (some areas)
• 10 ft from property line
• 25 ft from ignition sources

Local code varies; verify before placement.

Refilling logistics (propane)

• Local propane supplier provides scheduled refills
• "Keep full" service: supplier monitors, refills when 30% remaining
• Customer pays per delivery or per gallon
• Some suppliers offer remote monitoring + automatic refill

When to recommend each fuel

Recommend natural gas:

• Utility service available
• Customer wants no fuel management
• Indefinite runtime priority

Recommend propane:

• Rural / no natural gas
• Customer wants fuel independence
• Outage frequency high

Recommend gasoline (portable only):

• Short-duration outages
• Customer comfortable with refueling
• Lower budget

Recommend diesel:

• Very large loads
• Mission-critical (medical, business)
• Large fuel storage acceptable

Fuel system maintenance

For each fuel:

• Natural gas: annual inspection of supply line + pressure regulator
• Propane: tank inspection annually; regulator every 10 years
• Gasoline: drain + replace fuel every 6 months OR use stabilizer
• Diesel: water + sediment removal; fuel polishing for long-storage

References

• NFPA 54, 58, 110
• IFGC (International Fuel Gas Code)
• Manufacturer fuel pressure specifications
• Manuall internal: Generator Sizing for Residential, Whole-House Standby Generator Installation SOP