Why does a dual fuel generator produce less wattage on propane than gasoline?

Propane has approximately 10% to 15% less energy density per unit volume compared to gasoline (91,500 BTU per gallon for propane vs 114,000 BTU per gallon for gasoline). Additionally, gaseous fuel displaces more air in the intake manifold, reducing volumetric engine efficiency.

How much power do tri-fuel generators lose on natural gas?

Generators typically lose 18% to 22% (average 20%) of their rated gasoline wattage when running on utility natural gas. This derating is due to the lower energy density of natural gas (~1,030 BTU per cubic foot) and atmospheric gas pressure delivery.

How long will a 20 lb propane tank run a dual fuel generator?

A standard 20 lb BBQ propane tank contains roughly 4.7 gallons of usable fuel (17.5 lbs). On a 7,500W generator running at 50% load (consuming ~0.9 to 1.1 GPH), a 20 lb tank lasts about 4.5 to 5.5 hours. On a smaller 3,500W inverter generator, it can last 12 to 16 hours.

Which fuel is cheapest to run: Gas, Propane, or Natural Gas?

Utility Natural Gas is almost always the cheapest fuel option per hour (often 50% to 70% cheaper than gasoline or delivered propane) because it is piped continuously at low residential utility rates without delivery fees or cylinder refills.

Can I convert my standard gasoline generator to dual or tri-fuel?

Yes. Aftermarket tri-fuel carburetor conversion kits or demand regulator kits (like Garretson KN style low-pressure regulators) allow most 4-stroke small engine generators to run on LPG and Natural Gas safely.

Dual & Tri-Fuel Multi-Energy Calculator

Dual Fuel & Tri-Fuel Generator Calculator

Compare power derating (wattage loss), starting & running load limits, hourly fuel consumption rates, runtime across all tank sizes, and operating cost per kWh between Gasoline, Liquid Propane (LPG), and Natural Gas (NG).

Share Tool:

1 Select Active Fuel Type

Derate Auto-Calculated

Choose the fuel you are operating on to automatically apply output derating and calculate hourly burn rate:

2 Generator Baseline Capacity (Gasoline Rating)

Nameplate Specs

Quick Size Presets (Click to Select): Default (7.5kW)

Running / Continuous Watts (Gas)

Starting / Surge Watts (Gas)

3 Target Electrical Load Demand

Load Simulation

Continuous Power Draw / Load:

Watts

4 Fuel Tank Supply & Local Energy Prices

Customizable

Propane Tank Size (Runtime Calculation)

Gasoline Tank / Can Capacity

Gasoline ($/Gallon)

Propane ($/Gallon)

Natural Gas ($/Therm)

Propane / LPG Mode 90.0% of Baseline

Effective Continuous Power

6,750 Watts

Peak Surge: 8,550 W • Power Loss: -750 W

Generator Load Utilization: 66.7% (Safe Zone)

0% 50% (Optimum) 80% (Max Cont.) 100%

Hourly Cost $3.82 / hr $0.85 / kWh

Fuel Burn Rate 1.18 GPH 4.99 lbs/hr

Supply Runtime 20.0 Hours 0.8 Days (100lb Tank)

24-Hour Outage Cost $91.68 / day 28.3 Gal Total

Winter Operation & Fuel Flow Advisory

Gas vs. Propane vs. Natural Gas Comparison Matrix

Side-by-side performance calculations for your 7,500W generator at 4,500W load.

Real-Time Dynamic Data

Performance Metric	Gasoline (100%)	Propane LPG (90%)	Natural Gas NG (80%)

Operating Cost & Fuel Consumption by Load Level

Visual comparison of hourly running cost ($/hr) across 25%, 50%, 75%, and 100% generator electrical loads.

Dual-Fuel & Tri-Fuel Formulas & Reference Chart

Standard engineering equations and fuel heating values used to calculate power derating, fuel consumption, and backup runtimes.

Engineering Specs

1. Fuel Energy Density & Heating Values

The primary reason engines produce different horsepower and electrical wattage on different fuels is the Higher Heating Value (HHV) and energy density per unit volume of fuel inducted into the combustion chamber:

Fuel Type	Energy Density (BTU)	Output Derate vs. Gas	Storage Shelf Life	Carburetor Gumming
Gasoline (Unleaded E10)	114,000 BTU / gallon	0% (Baseline 100%)	3 - 6 Months (Ethanol degrades)	High Risk (Requires stabilizer/drain)
Liquid Propane Gas (LPG)	91,500 BTU / gal (21,548 BTU/lb)	~10% Derate (90% Power)	30+ Years (Indefinite in tanks)	Zero Risk (Clean vapor burn)
Natural Gas (Utility Methane)	100,000 BTU / Therm (1,030 BTU/cu.ft)	~20% Derate (80% Power)	Continuous Utility Supply	Zero Risk (Cleanest burning)