Generator Fuel Cost Per Hour 2026: Burn Rates, Runtime and Cost Per kWh

Quick answer

A 22 kW standby generator burns about 228 cubic feet of natural gas or 2.53 gallons of propane per hour at half load, which is roughly $4.52 or $6.76 an hour at September 2026 US average fuel prices, so about $108 or $162 for a full day of backup power. A 500 gallon propane tank holds 400 usable gallons under the NFPA 58 80 percent fill limit and runs that generator about 6.6 days at half load, or close to 9 days at the quarter load most houses actually draw. Smaller units cost far less per hour: a 10 kW runs about $2.00 an hour on natural gas.

Generator fuel consumption and cost per hour by size (2026)

This is the table worth bookmarking. Burn rates come straight from Generac Guardian and PowerPact spec sheets, which publish consumption at half load and full load only. The dollar columns apply the current US average fuel prices: natural gas at $19.83 per thousand cubic feet (EIA, May 2026, the latest monthly residential figure) and propane at $2.67 per gallon (EIA residential survey, week ending 30 March 2026, the last published price before the survey pauses each April through September).

Burn rates: Generac Guardian and PowerPact published spec sheets (10-16 kW, 14-18 kW, 20-24 kW and 26 kW sheets, 2025 and 2026 revisions). Prices: EIA residential natural gas $19.83/Mcf (May 2026) and residential propane $2.67/gal (week ending 30 March 2026). Half load means half of rated output, so 11 kW for a 22 kW unit.

Why the bigger generator sometimes burns less

Read that table carefully and something looks wrong. The 18 kW burns 169 cubic feet of natural gas at half load while the 14 kW burns 195. The 26 kW burns 188 while the 22 kW burns 228. Bigger units using less fuel is not a typo in the spec sheet.

Two things are going on. First, half load means half of that unit's own rating, so the 14 kW figure is for 7 kW of output and the 18 kW figure is for 9 kW. Second, and more to the point, these are different engine platforms with different displacement and different generations of engine control. The 26 kW Guardian uses a newer 1.0 litre engine that is simply more efficient than the older 999cc unit under the 22 kW, and Generac revised that sheet in 2025. Per kilowatt-hour produced, the 26 kW at half load is the most efficient air-cooled unit on the chart.

The practical takeaway: do not assume the smaller generator is the cheaper one to run. If you are sizing a unit, compare the spec sheets for the exact model numbers your dealer is quoting rather than assuming kW maps to fuel burn. Our whole house generator sizing guide covers the load side of that decision, and the electrical load calculator gives you the demand number to size against.

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

Multiply the hourly figure by 24. Here is what a full day of outage costs on the common sizes, still at half load:

Those seven-day propane numbers are the reason people who live through a long outage end up asking hard questions about tank size. A week on a 22 kW at half load is 425 gallons, which is more than a full 500 gallon tank holds. On natural gas the same week is $759 and arrives on the monthly bill with no refill truck involved, which is the single biggest practical argument for a gas main connection if you have one available.

In practice most homes do not sit at half load for a week. Half load on a 22 kW is 11 kW continuous, which is a heat pump plus a well pump plus a range running together. A house riding out an outage with the HVAC cycling, a fridge, a freezer, lights and some outlets typically averages 4 to 7 kW, closer to a quarter load. That is why the next section matters more than the table above.

Does a generator use less fuel with a lighter load?

Yes, but not proportionally, and this is where nearly every runtime estimate on the internet goes wrong. People take the half-load figure, halve it again for quarter load, and get a runtime that is 30 percent too optimistic.

Fuel burn on a fixed-speed generator has two parts. One part scales with the electrical load. The other part is the cost of spinning a 999cc engine at 3,600 rpm whether or not anything is plugged in, and that part does not go away. Fit a straight line through the two published points and you can read the fixed part off the intercept:

Slope = (3.90 − 2.53) gal/hr ÷ 11 kW = 0.1245 gal/hr per kW
No-load intercept = 2.53 − (0.1245 × 11) = 1.16 gal/hr
At 25% load (5.5 kW) = 1.16 + (0.1245 × 5.5) = 1.85 gal/hr

So the 22 kW at quarter load uses 1.85 gallons per hour, not the 1.27 you get by halving. That is 46 percent more fuel than the naive estimate, and it turns a predicted 13 day run on a 500 gallon tank into a real 9 day run. The same arithmetic on natural gas gives a no-load intercept near 129 cubic feet per hour and about 178 cubic feet per hour at quarter load.

That fixed cost also explains the efficiency curve. Producing 5.5 kW costs $4.94 an hour on propane, which is $0.90 per kWh. Producing 11 kW costs $6.76, which is $0.61 per kWh. The generator gets cheaper per unit of energy the harder you work it, right up to about 80 percent load, which is the opposite of the instinct to run it light to save fuel.

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

The animation below runs the same 500 gallon tank against three load levels on a 22 kW Guardian. A 500 gallon tank is filled to 400 gallons because NFPA 58 caps residential fill at 80 percent, leaving vapor space for thermal expansion. That is the single most common mistake in tank runtime math.

Full runtime table for a 22 kW, covering the tank sizes propane companies actually install:

Based on 1.85, 2.53 and 3.90 gal/hr for a 22 kW Guardian. Fill cost at $2.67/gal on a full 80 percent fill, before delivery fees and tank rent. Scale the runtimes by the burn-rate ratio for other sizes: a 14 kW at half load uses 1.81 gal/hr, so multiply the 22 kW runtimes by about 1.4.

Three things the table does not show. Tank rent runs $60 to $200 a year if you lease rather than own, and leased tanks usually lock you to one supplier's pricing. Delivery minimums matter, since most companies will not send a truck for less than 100 to 150 gallons. And in cold weather a tank that is low on liquid struggles to vaporize fast enough to feed a generator at high draw, which is why installers size the tank for vaporization rate and not just for days of runtime. Below roughly 30 percent remaining on a 250 gallon tank at 0°F, a 22 kW at high load can outrun the tank's vapor supply.

How much gas does a portable generator use per hour?

Portables are gasoline unless they are dual fuel, and the numbers work differently. Manufacturers publish runtime on a full tank rather than gallons per hour, usually at 25 or 50 percent load, so you have to divide. At the EIA US average of $4.32 per gallon for regular gasoline (week of 14 September 2026):

The hours-per-tank column is the one that changes your life during an outage. A 9,500 watt portable running the essentials needs refueling every seven hours, which means getting up in the middle of the night, shutting it down, letting it cool, and pouring gasoline in the dark. Over a four day outage that is roughly 13 refills and 86 gallons, about $373 of fuel, assuming the stations near you still have power to run their pumps.

Inverter generators are the exception worth knowing. Because the engine speed tracks the load instead of sitting at a fixed 3,600 rpm, the fixed-burn penalty mostly disappears at light loads. A 2,200 watt inverter running a fridge and a few lights genuinely does sip fuel, and it is quiet enough to sleep next to. It is also useless for a well pump or central air.

Is generator power more expensive than grid power?

Far more, and the gap is bigger than most people expect. Divide the hourly fuel cost by the kilowatts actually being produced and you get a real price per kWh you can set next to your utility bill. The US residential average is 18.4 cents per kWh on EIA 2026 data.

Generator electricity costs roughly two to five times grid electricity, and that is fuel alone. Add oil and filter changes every 100 to 200 running hours, an annual service at $150 to $400, and the amortized cost of a $5,000 to $15,000 installed unit, and the true cost per kWh during a short outage can pass $2. None of that is an argument against owning one. It is an argument for treating a standby generator as insurance against spoiled food, frozen pipes and a house you cannot live in, rather than as a way to make power.

It is also why the load management question matters. Shedding the electric water heater and the clothes dryer during an outage cuts both the fuel bill and the size of unit you need. Run your numbers through the kWh calculator and the appliance energy calculator to see which circuits are doing the damage, and compare against what you normally pay using the electricity cost calculator.

Natural gas or propane: which should you run?

If a gas main runs past your house, natural gas is usually the answer. The comparison in full:

Diesel belongs in the conversation for larger liquid-cooled units. A 20 kW diesel burns roughly 0.8 gallons per hour at half load and 1.6 at full, which is efficient per kWh, but diesel needs fuel polishing or biocide treatment if it sits for a year, and residential diesel standby is rare below 30 kW. Pricing swings enough that it is worth pulling your local number rather than a national average.

The gas meter problem nobody warns you about

This is the install surprise that shows up after the generator is already sitting on the pad. Natural gas consumption is usually quoted in cubic feet per hour, and one cubic foot of natural gas carries roughly 1,000 BTU. A 22 kW at full load wants 327 cubic feet per hour, which is about 327,000 BTU per hour of additional demand on your gas service.

A typical older residential meter is rated 250 CFH, and it is already feeding a furnace at 80,000 to 120,000 BTU, a water heater at 40,000, a range at 65,000 and maybe a dryer at 22,000. Add the generator and the meter, the service regulator, or the piping cannot deliver it. The symptom is a generator that starts fine, carries the house for a minute, then stumbles and drops out when the furnace kicks on, because inlet pressure sagged below the 5 inches of water column the unit needs.

The fix is a utility meter and regulator upsize to 400 or 1,000 CFH, which most utilities do at no charge or a modest fee, plus correctly sized black iron or CSST from the meter to the unit. Ask your installer for the pipe sizing calculation before the job, not after. Propane has its own version of the same constraint, which is the tank vaporization rate mentioned earlier.

What does the weekly exercise cycle cost?

A standby generator self-tests on a schedule, typically 5 to 12 minutes once a week depending on model and controller setting. That is 4 to 11 hours a year, and the test runs unloaded or lightly loaded, near the no-load intercept of about 129 cubic feet per hour on natural gas or 1.16 gallons per hour on propane.

12 min/week × 52 weeks = 10.4 hr/year
Natural gas: 10.4 × 129 ft³ × $0.01983 = $26.60/year
Propane: 10.4 × 1.16 gal × $2.67 = $32.20/year

So roughly $25 to $35 a year, which is genuinely trivial next to the $150 to $400 annual service. Most controllers let you switch to a biweekly schedule or shorten the run, and Generac's quiet-test mode runs at a lower engine speed. Do not disable it. The exercise cycle is what keeps the battery charged, circulates the oil and catches a dead starter battery in June rather than during a January ice storm. A generator that has not run in eight months is a generator you find out about at the worst possible moment.

The costs that are not fuel

Fuel is the number people search for, and it is rarely the largest line. Running total for a 22 kW air-cooled standby over a year with two short outages:

Call it $700 to $1,300 a year all in, of which fuel is maybe 15 percent. The install side of that is worth understanding before you buy, since transfer switch work, a possible service upgrade and the electrician's time move the number more than the generator does. See the panel upgrade cost calculator and electrician rate calculator for local labor pricing, and how many amps a house actually uses if you are deciding between whole-house and essential-circuits coverage.

Code and safety notes before you run anything

Transfer equipment is not optional. NEC Article 702 covers optional standby systems, and 702.5 requires listed transfer equipment so the generator cannot backfeed the utility. Backfeeding through a dryer outlet with a double-male cord, the so-called suicide cord, energizes the utility drop and can kill a lineman working to restore your power. It also bypasses every overcurrent protection in the path. Article 702.4 covers capacity and 702.7 covers the required signage at the service.

Carbon monoxide kills people every single storm season. A portable generator never runs indoors, in a garage with the door open, in a crawlspace, or under a deck. CPSC multi-year data attributes roughly 85 consumer deaths a year to CO from portable generators, most of them from units placed in or against a house. Twenty feet from the building with the exhaust pointed away is the standard guidance, and a working CO alarm on every level is not negotiable.

Clearances. NFPA 37 sets a default of 5 feet from openings and combustible walls for stationary engines, though most manufacturers have bought reduced clearances by fire test and publish 18 inches in their install manuals. NFPA 58 requires a minimum of 10 feet between a stationary propane tank of 125 to 500 gallons and any building, property line, or ignition source, which includes the generator itself.

Fuel handling. Never refuel a hot portable. Let it cool for several minutes, because spilled gasoline on a hot muffler is the second most common generator injury after CO. Store gasoline in approved containers away from the house and treat it with stabilizer if it will sit past a few months.

Electrical work carries safety and legal risk. Verify any calculations here with a licensed electrician familiar with your local code before performing work. This article references NEC 2023. Many jurisdictions operate under earlier editions or local amendments, so verify with your local AHJ. Fuel burn rates are manufacturer test-condition ratings and your real consumption will differ with altitude, ambient temperature, fuel pressure, engine condition and how your loads cycle.

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Related reading: whole house generator sizing, why your electric bill is so high, US electricity cost by state, and whole house surge protector cost.

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