Generac Generator Fuel Consumption: Natural Gas & Propane by Size

Current Generac Fuel Consumption Table

These are manufacturer ratings, not a promise of what every installed generator will consume.

Actual use changes with load.

Natural Gas: What the Numbers Mean

Natural gas consumption is usually listed in:

cubic feet per hour — ft³/hr

If a 22kW Generac is using 221 ft³/hr at 50% load, then ten hours at that load would consume roughly:

2,210 cubic feet

At full rated load, the same current model is published at about:

311 ft³/hr

The generator does not simply use the full-load number every hour.

Your actual house load matters.

Propane: What the Numbers Mean

Propane fuel consumption is usually easier for homeowners to understand in:

gallons per hour

A current 18kW Generac is published at approximately:

• 1.65 gal/hr at 50% load
• 2.87 gal/hr at full load

A current 28kW is approximately:

• 2.23 gal/hr at 50% load
• 3.97 gal/hr at full load

That is a large difference over a multi-day outage.

How Long Will a 500-Gallon Propane Tank Run a Generac?

A nominal 500-gallon propane tank is not normally filled to 500 usable gallons.

Propane tanks are generally filled below total water capacity to leave room for expansion.

For rough planning, if you had about 400 gallons available:

18kW at 50% Load

400 ÷ 1.65 ≈ 242 hours

or about:

10 days

22kW at 50% Load

400 ÷ 2.45 ≈ 163 hours

or about:

6.8 days

28kW at 50% Load

400 ÷ 2.23 ≈ 179 hours

or about:

7.5 days

Those are mathematical estimates only.

Real runtime depends on:

• Starting fuel level
• Actual load
• Weather
• Tank vaporization
• Generator cycling
• Other propane appliances

Why Bigger Does Not Always Mean More Fuel at 50% Load

The current published fuel data is not a perfectly linear curve.

For example, the current 26kW and 28kW units can show similar or even lower published natural-gas consumption at 50% load than some smaller models.

That does not mean a 28kW generator is always cheaper to run than a 22kW.

It means:

engine platform + calibration + actual operating load matter.

Compare the exact model and the load you expect to carry.

Natural Gas vs Propane Fuel Consumption

Natural gas is normally measured in cubic feet.

Propane is normally measured in gallons.

The better question is not:

Which one uses fewer units?

The useful comparison is:

• Fuel availability
• Installed fuel-system capacity
• Local fuel price
• Runtime during outages
• Tank storage if propane
• Generator output on each fuel

Some Generac models also produce less electrical power on natural gas than propane.

Current Fuel-Specific Output Matters

Examples from the current Generac air-cooled lineup:

• 10kW: 10 kW LP / 10 kW NG
• 14kW: 14 kW LP / 14 kW NG
• 18kW: 18 kW LP / 17 kW NG
• 22kW: 22 kW LP / 21 kW NG
• 26kW: 26 kW LP / 24 kW NG
• 28kW: 28 kW LP / 25 kW NG

So if you are sizing a generator for natural gas, do not automatically use the propane headline rating.

How Much Natural Gas Does a 22kW Generac Use?

For the current 22kW Generac:

• About 221 ft³/hr at 50% load
• About 311 ft³/hr at full load

Published maximum output:

• 22 kW LP
• 21 kW NG

Read the Generac 22kW guide →

How Much Propane Does a 22kW Generac Use?

Current published figures:

• About 2.45 gal/hr at 50% load
• About 3.71 gal/hr at full load

That can consume a meaningful amount of propane during a 48-72 hour outage.

How Much Fuel Does a 26kW Generac Use?

Current 26kW published figures:

Natural Gas

• 182 ft³/hr at 50%
• 316 ft³/hr at 100%

Propane

• 2.05 gal/hr at 50%
• 3.95 gal/hr at 100%

Read the Generac 26kW guide →

How Much Fuel Does a 28kW Generac Use?

Current 28kW published figures:

Natural Gas

• 182 ft³/hr at 50%
• 297 ft³/hr at 100%

Propane

• 2.23 gal/hr at 50%
• 3.97 gal/hr at 100%

Read the Generac 28kW guide →

Fuel Use During a 24-Hour Outage

To estimate daily use:

hourly consumption × 24

Example: current 22kW at 50% propane load:

2.45 × 24 = 58.8 gallons/day

Current 18kW at 50%:

1.65 × 24 = 39.6 gallons/day

That difference matters if your propane tank is the limiting factor.

Why Load Management Saves Fuel

A standby generator does not need to run every high-demand appliance at the same time.

Load management can reduce peaks from:

• HVAC
• Water heating
• Pool equipment
• Dryer
• Second AC unit

Lower load generally means lower fuel use.

Calculate your generator size →

Does Exercise Use Much Fuel?

Not compared with a multi-day outage.

Current Generac standby units exercise for a short scheduled period.

Over a full year, the fuel used in exercise is usually minor compared with the fuel burned during even one long outage.

Fuel Pressure Still Matters

A generator can have plenty of theoretical gas available and still perform badly if the installed fuel system cannot supply the required:

• Pressure
• Pipe capacity
• Meter capacity
• Regulator capacity

Fuel consumption tables are also useful sizing data for the installer.

Read Generac gas pressure requirements →