Beyond the upfront installation cost, running your generator during an actual outage has its own ongoing fuel cost — one that’s easy to overlook until you’re facing a multi-day outage and wondering how much fuel (and money) it’s actually consuming.
Quick Estimate by Fuel Type and Size
| Generator Size | Natural Gas (per day, moderate load) | Propane (per day, moderate load) |
|---|---|---|
| 7-11kW | $3 – $8 | $12 – $25 |
| 14-20kW | $6 – $15 | $20 – $45 |
| 22-24kW | $8 – $20 | $28 – $60 |
These figures assume moderate load (not running at 100% capacity continuously) and current average fuel pricing, which varies by region and fluctuates over time.
Why Natural Gas Is Cheaper Per Day Than Propane
Natural gas is generally priced lower per unit of energy than propane in most U.S. markets, which is the main reason natural gas systems cost less to run day-to-day, even though the generators themselves and installation costs are often similar between the two fuel types. For a full comparison of the tradeoffs beyond just running cost, see our fuel type comparison guide.
How to Estimate Your Own Daily Running Cost
- Find your generator’s fuel consumption rate at 50% load (usually listed in the owner’s manual or manufacturer spec sheet) — this is a more realistic estimate than the rate at 100% load, since most households don’t run at full capacity continuously
- Multiply by your local fuel price (per therm/CCF for natural gas, per gallon for propane)
- Multiply by estimated hours of daily use — if you’re running the generator continuously (24 hours) versus only during specific hours, your actual cost will differ significantly
What Actually Drives Your Running Cost Up or Down
How much of the generator’s capacity you’re actually using
Running near full capacity (all circuits, central AC constantly cycling) burns meaningfully more fuel than running a managed, essential-circuits-only load. This is part of why some homeowners choose to run selectively rather than powering literally everything during an extended outage.
Local fuel pricing
Natural gas and propane prices vary by region and fluctuate seasonally — checking current local rates gives a more accurate estimate than relying on national averages.
Generator size relative to your actual load
An oversized generator running well below its capacity is often slightly less fuel-efficient per unit of power delivered than a properly sized unit running closer to its efficient operating range — another reason correct sizing matters beyond just upfront cost.
Budgeting for a Multi-Day Outage
For hurricane or extended winter storm scenarios, it’s worth budgeting for several days of continuous or near-continuous running. Using the daily estimates above:
- A mid-size 14-20kW natural gas system running for 5 days might cost roughly $30-$75 in fuel
- The same system on propane for 5 days might run $100-$225, depending on load and local pricing
This is a meaningful difference for homeowners in hurricane-prone regions planning propane tank sizing — worth factoring into both your fuel budget and how large a tank you choose to install.
Frequently Asked Questions
Is it cheaper to run a generator only part of the day rather than continuously? Yes — running only during hours when you actually need specific circuits (rather than 24/7) directly reduces fuel consumption, though it requires manually managing when the generator runs unless your system is set up for scheduled operation.
Does generator brand affect fuel efficiency? Somewhat — engine efficiency varies between brands and models, but load management (how much of the generator’s capacity you’re actually using) generally has a bigger impact on cost than brand-specific efficiency differences.
How do I know my generator’s exact fuel consumption rate? Check your specific model’s spec sheet or owner’s manual — manufacturers typically publish fuel consumption figures at both 50% and 100% load for natural gas and propane separately.
Bottom Line
Running cost during an outage is a real, if often overlooked, part of generator ownership — typically a few dollars a day for natural gas systems and meaningfully more for propane, scaling with generator size and how much of the home’s load you’re actually running. Budgeting for this ahead of an extended outage, especially propane tank sizing for multi-day scenarios, avoids an unpleasant surprise mid-outage.