When it comes to ensuring a steady power supply during outages, backup generators have become increasingly indispensable. However, the focus often shifts to power output capacities, sidelining an equally crucial aspect: fuel efficiency. This is particularly vital if you’re working with finite fuel resources like Liquid Propane (LP). In this comprehensive guide, we’ll delve into the complexities of fuel consumption in backup generators—both air-cooled and liquid-cooled. As a company that has been a trusted name in residential and commercial generators since 1968, Benfield Electric is well-equipped to guide you through this often-overlooked facet of generator ownership.

The Basics: Types of Generators

Generac Air Cooled Generator

Generac Air Cooled Generator

Air-Cooled Generators

These generators use air to dissipate heat from the system. Generally more suitable for smaller residential setups, air-cooled generators in the United States operate at a constant speed of 3600 RPMs and have a power output capped at 26 kW.

Liquid-Cooled Generators

Contrastingly, liquid-cooled generators employ coolant, much like the cooling system in an automobile. They tend to be more robust, quieter, and better suited for larger commercial applications. While they most commonly operate at a slower speed of 1800 RPM, some specialized models run at 3600 RPM for quicker power response, albeit at a higher fuel consumption rate.

Understanding Fuel Consumption

For Air-Cooled Generators:

Natural Gas Consumption

  • Half-Load: Ranges from 101,000 BTU for a 10 kW unit up to 169,000 BTU for an 18 kW model.
  • Full-Load: Peaks at 333,000 BTU for a 26 kW model.
Natural Gas (NG) Fuel Consumption Table in BTUs
Size Half Load Full Load
10 kW 101,000 127,000
14 kW 195,000 256,000
18 kW 169,000 247,000
20 kW 164,000 287,000
22 kW 204,000 327,000
24 kW 203,000 306,000
26 kW 188,000 333,000
*Data from Generac Air Cooled Generator Spec Sheets

Propane Consumption

  • Half-Load: As low as 0.97 gallons per hour for a 10 kW unit.
  • Full-Load: As high as 3.9 gallons per hour for a 22 kW and 24 kW unit.
Propane (LP) Fuel Consumption Table in Gallons per Hour
Size Half Load Full Load
10 kW .97 1.48
14 kW 1.81 3.07
18 kW 1.7 3.02
20 kW 2.36 3.74
22 kW 2.53 3.9
24 kW 2.53 3.9
26 kW 2.06 3.63
*Data from Generac Air Cooled Generator Spec Sheets

Two Ranges of Power Output

Air Cooled Generators Power Output Comparison on Natural Gas (NG) vs Propane (LP)

Air Cooled Generators Power Output Comparison on Natural Gas (NG) vs Propane (LP)

Air-cooled generators essentially operate in two modes: half-load for power output less than 50% and full-load for output greater than 50%. This is crucial when estimating fuel usage, especially during extended periods of use.

The Fuel-Type Output Discrepancy

When using natural gas, some models output less power compared to using propane. For example, a 20 kW model operating on propane can go down to 18 kW when using natural gas. This is a crucial point to consider when selecting your fuel type.

For Liquid-Cooled Generators:

Natural Gas Consumption

  • 25% Load: Starts at 100,000 BTU for a 22 kW unit.
  • 100% Load: Goes up to 1,063,000 BTU for an 80 kW unit.
Natural Gas (NG) Fuel Consumption Table in BTUs
Size 25% Load 50% Load 75% Load 100% Load
22 kW 100,000 190,000 255,000 316,000
27 kW 108,000 197,000 287,000 359,000
32 kW 144,000 226,000 298,000 375,000
38 kW 162,000 255,000 345,000 437,000
48 kW 201,000 336,000 447,000 604,000
60 kW 257,000 432,000 618,000 808,000
80 kW 292,000 534,000 799,000 1,063,000
*Data from Generac Air Cooled Generator Spec Sheets

Propane Consumption

  • 25% Load: As low as 1.1 gallons per hour for a 22 kW unit.
  • 100% Load: As high as 10.8 gallons per hour for an 80 kW unit.
Propane (LP) Fuel Consumption Table in Gallons per Hour
Size 25% Load 50% Load 75% Load 100% Load
22 kW 1.1 2.1 2.8 3.4
27 kW 1.2 2.1 3.1 3.9
32 kW 1.7 2.7 3.7 4.6
38 kW 1.7 2.9 4 5.2
48 kW 2.88 4.16 5.28 6.61
60 kW 2.1 4.4 6.8 8.4
80 kW 2.6 5.7 8.3 10.8
*Data from Generac Air Cooled Generator Spec Sheets

Four Ranges of Power Output

Unlike air-cooled units, liquid-cooled generators offer four distinct ranges of power output, allowing for greater control over fuel consumption.

Key Considerations

Minimum LP Tank Requirements

If you’re relying on LP, it’s crucial to heed the installation guidelines, which often recommend a minimum LP tank size of 250 gallons. This is a safeguard against running out of fuel, especially during prolonged outages.

Weather and Fuel Efficiency

It’s important to note that cold weather conditions can slow down the evaporation rates of LP, affecting its conversion from a liquid state to a gas state. Hence, in colder climates, you might need to account for higher fuel consumption rates.

Fuel Conservation Strategies

Planned Shutdowns

Generac Liquid Cooled Generator

Generac Liquid Cooled Generator

Turning off your generator at predetermined times, like overnight, can substantially reduce fuel consumption. See our article on Shutdown & Restart Your Generac Generator Safely.

Load Management

Invest in smart load management devices that can automatically prioritize essential loads during a power outage.

Regular Maintenance

Efficient operation often hinges on how well your generator is maintained. From changing filters to checking connections, regular upkeep can result in marginal yet significant fuel savings.

Brand Considerations

Different brands and models offer varying degrees of fuel efficiency. Therefore, take time to compare different options. At Benfield Electric, we offer a range of brands, each with its pros and cons, to help you make an informed choice. Check out our other article on Generator Comparison Generac vs Cummins vs Kohler vs Briggs to learn more about this.

How Benfield Electric Can Help You

Having been in business since 1968, we’ve installed thousands of units across Northern Virginia, Maryland, and Washington, D.C. We carry an extensive inventory of generators, parts, and accessories needed for the upkeep of your unit.

With our vast experience, we’re ideally placed to guide you through your generator purchase journey, from selecting the right model and size to understanding the nuances of fuel efficiency. We even offer comprehensive installation and maintenance services to ensure that your unit performs at its best.


Choosing a backup generator is not just about power output. Several variables, including fuel consumption and efficiency, play crucial roles in making an informed decision. At Benfield Electric, we’re committed to helping you navigate these intricacies. Your peace of mind is our ultimate aim, and we take this responsibility seriously.

Feel free to contact us for comprehensive consultation services, and rest assured that you’re in capable hands. When you choose wisely, you not only save on fuel but also invest in a reliable, durable power solution that stands the test of time.

By understanding the ins and outs of fuel consumption in backup generators, you’re better equipped to make an informed decision that not only meets your immediate needs but also factors in long-term operational costs. Trust Benfield Electric to guide you through this complex yet essential aspect of owning a backup generator.

For more resources and insights into the world of backup generators, stay tuned to our blog and articles or contact us! We’re here to help you make the best choices for a reliable, fuel-efficient, and long-lasting power solution.