Natural Gas vs Propane Generators: Which Fuel Type Is Right for Your Home?

If you have natural gas at your house, use natural gas. Seriously. It's cheaper, the supply doesn't run out, and there's no tank sitting in your yard. Decision made.

If you don't have gas service — common in rural areas — propane is your fuel and it works great. You'll need a tank, and you'll need to keep it filled, but plenty of homeowners run standby generators on propane for decades without issue.

That's the short version. If you want to understand why, or if you're in one of the edge cases where it's actually a close call, keep reading.

What It Costs to Run

Natural gas wins on cost. Not by a huge margin, but consistently, about 20 to 30% cheaper than propane across most of the country.

These numbers use current national averages from the U.S. Energy Information Administration: natural gas at $14.09 per MCF and propane at $2.68 per gallon.

Most outages don't hammer the generator at full load around the clock. Half load is more realistic; the AC cycles, you're not running the oven and dryer simultaneously. At half load, the fuel cost difference shrinks to about $8 per day. Real money over a week-long outage, but not life-changing.

The weekly exercise run — that 15 to 30 minutes of automatic self-testing — costs about a dollar a week on either fuel. Don't factor exercise fuel into your decision. It's noise.

Generators Produce Less Power on Natural Gas (This Surprises People)

Most generators put out about 10% less on natural gas than on propane. A unit rated at 22 kW on propane delivers roughly 19.5 to 20 kW on natural gas.

Why? Energy density. One cubic foot of propane packs 2,516 BTU. Natural gas: 1,030 BTU. Propane has nearly two and a half times the energy per volume. The generator's engine simply has less fuel energy to work with on NG.

Every brand shows this in their specs:

One notable exception: Briggs & Stratton's NGMax technology. Their 22 kW PowerProtect delivers 22 kW on both fuels. It's one of the only generators in the industry where the NG output matches propane.

Does the 10% drop actually matter day to day? For most homes, no. Generators are sized with headroom, and the derating is already baked into the manufacturer's sizing recommendations. But if you're tight on sizing — big AC, lots of loads, generator barely covering the math — that 10% could mean the difference between running smoothly and tripping the breaker when the compressor kicks on. In that case, just step up one size. The difference between a 20 kW and 22 kW unit is a few hundred bucks. Undersizing costs you sleep.

Reliability During Disasters

This is where the conversation gets real. Cost and output are nice to know. What happens when everything goes wrong is what actually matters.

Natural Gas

Underground pipelines. That's the key advantage. Wind, rain, falling trees, surface flooding: none of it touches gas lines buried underground. The American Gas Association says only 1 in 650 customers loses gas service in any given year.

As long as the pipeline holds, your fuel is unlimited. No tank gauge to watch, no delivery truck to wait for, no anxiety about running out on day five of a hurricane. The gas just flows.

Where it breaks down: earthquakes and extreme cold. Fault movement can rupture pipelines. Winter Storm Uri in 2021 proved that extreme cold can freeze wellheads at the source, cutting supply to millions in Texas. But for the storms and ice events that cause most outages? Natural gas infrastructure holds up.

Propane

Your fuel is sitting in your yard in a tank. It doesn't care what the utility company is doing. It doesn't care if the roads are washed out. It doesn't need infrastructure to work: it's already there.

You can fill the tank before hurricane season in September or before winter in October. When the outage hits, you're ready regardless of what happens to the grid, the roads, or the gas company.

The limitation is math. A 500-gallon tank holds about 400 usable gallons (80% fill rule for thermal expansion). A 20 kW generator at typical household usage burns roughly 36 gallons a day. That gives you 7 to 11 days of continuous operation: more than enough for the vast majority of outages. But for a Puerto Rico-scale event lasting weeks or months, you'd need deliveries. And if roads are impassable, deliveries aren't coming.

So Which Is More Reliable?

For most disasters — hurricanes, ice storms, grid failures — natural gas wins. The supply is unlimited and the infrastructure almost always survives.

For total independence from infrastructure: earthquake zones, extreme rural areas, anywhere you don't trust the utility: propane wins. Your fuel doesn't depend on anyone else.

Most homeowners with gas service should use gas. Most homeowners without gas service have no choice but propane, and that's perfectly fine.

Propane Tanks

If you're going the propane route, you need a tank. The standard recommendation for standby generators is a 500-gallon tank.

A few things to know:

Cost: $1,000 to $2,000 for above-ground installation. $1,500 to $2,500 to bury it underground. A full fill runs about $1,072 at current national average pricing.

Runtime: 7 to 11 days of continuous operation on a 20 kW generator. More than enough for any typical outage.

Placement: Tanks over 100 gallons must sit at least 10 feet from any building. Plan your yard layout with both the tank and generator in mind: they can't be right next to each other.

Rental option: Many propane companies lease tanks for free or a small annual fee if you agree to buy fuel exclusively from them. Saves you $1,000 to $2,500 upfront, but you're locked into one supplier's pricing. Worth it for some people, not for others. Ask your propane company what they offer before buying a tank outright.

Do You Even Have a Choice?

About 61% of U.S. households use natural gas. Roughly 73% have access even if they're not currently using it. That means about 27% of homes — mostly rural — have no gas option at all.

If you're in that 27%, the decision is already made. Propane. Done.

If you have gas service, use gas. The only exception worth thinking about is if you're in a serious earthquake zone. California's San Andreas corridor, the Pacific Northwest's Cascadia zone: where pipeline integrity during a major seismic event is a genuine question. Even then, most people still go with gas.

Building new or not sure what fuel you'll have? Buy a dual-fuel generator and figure it out at installation.

What "Dual-Fuel" Actually Means

Every time you see "dual-fuel" on a generator spec sheet, it means the unit runs on either natural gas or propane. Not both at once: one or the other, configured at installation.

Your installer sets the fuel orifice and adjusts the settings for whichever fuel you're connecting to. If you ever need to switch — say you had propane but gas service comes to your street — a technician can reconfigure it.

All five major brands offer dual-fuel across their entire residential lineup. Generac, Kohler, Cummins, Briggs & Stratton, Champion. It's not an upgrade or an add-on. It's just how standby generators are built now.

Environmental Difference (Brief)

If you're factoring this in: natural gas emits about 117 pounds of CO2 per million BTU. Propane emits 139, roughly 14% more. Natural gas is cleaner on direct emissions.

The wrinkle is upstream methane. Natural gas production and distribution leak methane, which is 28 times more potent than CO2 over a century. Factor that in and the gap between the two fuels narrows considerably.

Both are significantly cleaner than diesel or gasoline. Propane is classified as a "clean energy source" under the 1990 Clean Air Act. For most homeowners, the environmental difference between these two fuels isn't meaningful enough to override cost and availability.

Which Fuel Should You Choose?

Honestly, for 90% of the people reading this: if you have gas, use gas. If you don't, use propane. The edge cases above matter for maybe 10% of buyers. Everyone else can stop overthinking this and move on to sizing.

Figure Out Your Size, Then Worry About Fuel

The fuel choice is easy. The sizing question is where most people actually get stuck.

What size generator do you need? →

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Content reviewed for technical accuracy by a licensed electrician. OffGrid Compare is independent — we don't sell generators or represent any brand. Our story →