How Much Does It Cost to Run a Whole House Generator? Fuel Use and Runtime

Quick answer: A typical whole house standby generator costs roughly $1 to $4 per hour to run on natural gas and about $3 to $9 per hour on propane at half load, depending on size and local fuel prices. A multi-day outage usually lands between about $50 and $600 in fuel. These are estimates; your cost depends on generator size, how much of the house you power and what fuel costs in your area.

If you are shopping for backup power or already own a standby unit, knowing the hourly operating cost helps you budget for outages and choose the right fuel. This guide breaks down how much it costs to run a whole house generator, with fuel use figures, outage scenarios and ways to spend less. If you want help comparing options, you can request free backup power quotes using the form on this page.

How Much Does a Generator Cost to Run Per Hour?

Standby generators burn fuel in proportion to the electrical load they carry. A 22 kW unit powering only a few circuits uses far less than the same unit running central air, an electric range and a dryer at once.

Manufacturers publish fuel consumption at 50% and 100% load. The figures below are typical ranges for common residential sizes, offered as estimates. Check the spec sheet for your exact model.

• Natural gas, 50% load: about 80 to 190 cubic feet per hour for 14 to 24 kW units.
• Natural gas, full load: about 150 to 330 cubic feet per hour.
• Propane, 50% load: about 1.5 to 3.5 gallons per hour.
• Propane, full load: about 2.5 to 5.5 gallons per hour.

Natural gas is billed by the therm or cubic foot, and one therm is roughly 100 cubic feet. With gas at around $1.00 to $2.00 per therm in many areas, a mid-size generator at half load costs roughly $1 to $4 per hour. Propane at about $2.50 to $4.50 per gallon puts the same load at roughly $4 to $15 per hour, though most homes land lower because they rarely run near full load.

Natural Gas vs Propane: Fuel Use and Cost Comparison

Propane contains less energy per unit of volume than most people expect, and generators burn more of it for the same output. That is why the per-hour cost runs higher even though the generator itself is identical or nearly so.

Typical cost per hour (estimates)

• 14 to 16 kW at 50% load: natural gas about $1 to $2.50; propane about $4 to $8.
• 22 to 24 kW at 50% load: natural gas about $1.50 to $3.50; propane about $5 to $10.
• Full load, large unit: natural gas about $3 to $6; propane about $9 to $16.

Natural gas also removes refueling worries because the utility line keeps supplying it, though supply can occasionally be affected in major disasters. Propane depends on tank capacity, so runtime is a math problem. For a deeper look at reliability and price trade-offs, see our comparison of natural gas vs propane standby generators.

What the generator powers matters more to your fuel bill than how big the generator is.

Propane Tank Size and Generator Runtime

With propane, the question shifts from cost to how long the fuel lasts. Tanks are typically filled to about 80% of capacity, so usable gallons are lower than the label suggests.

Rough runtime estimates for a 22 kW generator at half load, using about 2.5 to 3 gallons per hour:

• 250-gallon tank (about 200 usable gallons): roughly 65 to 80 hours, or about 3 days.
• 500-gallon tank (about 400 usable gallons): roughly 130 to 160 hours, or about 5 to 6 days.
• 1,000-gallon tank: well over a week at moderate load.

At lighter loads, such as overnight when only the refrigerator, furnace fan and a few lights are running, those runtimes stretch considerably. Generators also cycle, so real-world use is often less than continuous full output. If you are sizing equipment, our generator sizing guide and load worksheet shows how to estimate your actual draw.

Example Outage Cost Scenarios

These scenarios use estimated fuel prices of $1.50 per therm for natural gas and $3.50 per gallon for propane. Your numbers will vary.

Scenario 1: 24-hour storm outage, moderate load

• A 22 kW generator at about 50% load.
• Natural gas: roughly 24 hours at $2 to $3 per hour, or about $50 to $75.
• Propane: roughly 24 hours at $8 to $10 per hour, or about $190 to $240.

Scenario 2: 3-day winter outage, whole house

• Electric heat or a heat pump drives higher load, closer to 60 to 75%.
• Natural gas: about 72 hours at $3 to $4.50 per hour, or about $215 to $325.
• Propane: about 72 hours at $10 to $13 per hour, or about $720 to $940, with a 500-gallon tank covering most of it.

Scenario 3: 7-day extended outage, essentials only

• Lights, refrigerator, furnace, well pump and electronics at roughly 25 to 35% load.
• Natural gas: about $1 to $2 per hour, or roughly $170 to $340.
• Propane: about $4 to $6 per hour, or roughly $670 to $1,000.

Even in the harder scenarios, fuel is a small fraction of what spoiled food, frozen pipes or a hotel stay would cost. If you also want a price on the equipment itself, read our guide to whole house generator cost installed.

Even a week-long outage typically costs a few hundred dollars in fuel, far less than the damage it prevents.

Other Running Costs Beyond Fuel

Fuel is the biggest variable cost during an outage, but a standby generator has ongoing expenses that apply whether or not the power goes out.

• Maintenance: annual service commonly runs about $150 to $400, depending on the dealer and what is replaced.
• Oil and filters: changed at intervals set by run hours or yearly, whichever comes first.
• Weekly exercise cycle: most units self-test for about 5 to 20 minutes, using a small amount of fuel each week.
• Battery replacement: typically every few years.

The weekly exercise cycle adds up to a modest fuel cost across a year, usually a few dollars a month on natural gas. Setting the test for midday and keeping the generator clear of debris helps it start reliably when you need it. A transfer switch is what safely moves the house onto generator power, and it is a key piece of the installed system.

How to Lower Your Generator’s Fuel Consumption

You cannot control the length of an outage, but you can control the load. Because fuel use climbs steeply with demand, small habits make a real difference.

1. Stagger big appliances. Run the dryer, oven and dishwasher at different times rather than together.
2. Raise your AC setpoint. Moving the thermostat a few degrees in summer, or lowering it in winter, trims the largest single load.
3. Use a load management module. Smart load management devices automatically shed non-essential circuits when demand is high.
4. Switch to LED lighting and unplug idle electronics. Small savings add up over days.
5. Delay water heating. Electric water heaters are heavy loads; heat water in blocks, or turn the heater off during peak use.
6. Keep the generator serviced. A clean air filter and fresh oil keep it running efficiently.

Sizing matters too. An oversized generator is not necessarily more wasteful when lightly loaded, but running a smaller unit near its limit burns fuel inefficiently and strains the engine. Match the unit to your real needs, then manage the load during the outage.

If you are weighing a generator against other backup options, our comparison of portable vs standby generators covers running costs and convenience. You can also look into a generator maintenance checklist to keep operating costs down.

Ready to see what a system would cost to install and run at your address? Request your free generator quote with the form on this page and compare vetted providers with no obligation.

Frequently Asked Questions

How much does a generator cost to run for 24 hours?

For a typical whole house standby unit at moderate load, expect roughly $50 to $100 on natural gas and about $150 to $300 on propane. Heavy loads such as central air or electric heat push those figures higher. These are estimates based on average fuel prices.

Does a generator use less fuel at lower loads?

Yes. Fuel consumption drops as load decreases, though not perfectly in proportion. A generator at half load generally uses well under the fuel it burns at full load, so trimming demand is one of the best ways to save.

How long will a 500-gallon propane tank run a generator?

At moderate load, a 500-gallon tank typically lasts around 5 to 6 days, assuming it is filled to about 80%. At lighter loads it can last a week or more, and at heavy loads it may last closer to 3 days.

Is natural gas or propane cheaper to run a generator?

Natural gas is usually cheaper per hour, often by half or more. Propane costs more per hour but is a good fit for homes without a gas line, provided the tank is sized for the outages you expect.

Related: How Long Do Whole House Generators Last? Lifespan, Service Intervals and Replacement Signs