Natural Gas vs Propane for Standby Generators: Which Fuel Wins?

When you buy a standby generator, you're making two purchases: the machine and the fuel that feeds it. Most residential standby units — Generac, Kohler, Cummins — come configured to run on either natural gas or propane (many are dual-fuel capable out of the box or with a conversion kit), so the choice is yours. And it's a bigger decision than most buyers realize, because it affects your installation cost, your running cost, your cold-weather reliability, and what happens to your fuel supply during the exact emergency you bought the generator for.

When you buy a standby generator, you’re making two purchases: the machine and the fuel that feeds it. Most residential standby units — Generac, Kohler, Cummins — come configured to run on either natural gas or propane (many are dual-fuel capable out of the box or with a conversion kit), so the choice is yours. And it’s a bigger decision than most buyers realize, because it affects your installation cost, your running cost, your cold-weather reliability, and what happens to your fuel supply during the exact emergency you bought the generator for.

This article lays out the honest trade-offs with real numbers so you can pick based on your situation, not on a sales brochure.

Safety note up front: Everything involving fuel gas — gas line sizing, regulator installation, propane tank placement, leak checks — requires a licensed gas technician or plumber. Gas work done wrong doesn’t just fail; it can explode. This article is about choosing the fuel, not installing it.

How Each Fuel Actually Reaches Your Generator

Understanding the delivery path is the foundation of the whole comparison.

Natural gas arrives through underground utility pipelines at low pressure (typically around 0.25 PSI at the residential meter, regulated down further at the generator). Your generator connects to your home’s existing gas service through a dedicated line. There’s no tank, no delivery truck, no refills. The fuel is “always there” — as long as the utility’s system is functioning.

Propane is stored as a liquid under pressure in a tank on your property. The liquid boils into vapor inside the tank, and that vapor feeds the generator through a regulator. Typical residential setups use a 250-gallon, 500-gallon, or 1,000-gallon tank (those are nominal sizes — a 500-gallon tank actually holds about 400 gallons at the standard 80% fill). When the tank runs low, a delivery truck comes to refill it. You own or lease the tank, and you buy propane by the gallon.

This one difference — pipeline versus on-site storage — drives almost every trade-off below.

Fuel Availability During Outages: The Decisive Question

You’re buying a generator for outages. So the first question is: which fuel is more likely to be there when you need it?

Natural gas: rarely interrupted, but not invincible. Utility natural gas systems are pressurized underground networks. They don’t depend on the electric grid to deliver gas to your meter — the pressure comes from compressor stations, most of which have their own backup power. In ordinary storms, hurricanes, and ice events, natural gas service almost always stays on while the electricity is out. This is natural gas’s single biggest advantage: no refueling logistics during an extended outage.

But “almost always” isn’t “always.” Natural gas service can be interrupted:

In major earthquakes, utilities proactively shut off gas to damaged areas to prevent fires.
In severe flooding, gas infrastructure can be damaged or shut down.
During extreme cold events with record demand (like the February 2021 Texas freeze), utilities can curtail or interrupt service — some Texas neighborhoods lost gas pressure during that event.
If a gas main is damaged by construction or a vehicle strike near your home, your service stops until it’s repaired.

These are uncommon scenarios, but notice the pattern: the events that knock out natural gas tend to be the catastrophic, widespread disasters — exactly the ones where you’d most want your generator running.

Propane: independent, but finite. A propane tank is yours. No utility, no pipeline, no dependence on anyone else’s infrastructure. As long as there’s liquid propane in the tank, your generator runs — earthquakes, floods, and grid collapses don’t matter.

The catch is arithmetic: the tank holds a fixed amount of fuel, and a standby generator drinks it fast. A typical 22 kW standby generator burns roughly:

Load	Propane consumption	500-gal tank (400 usable gal) runtime
Half load (~11 kW)	~2.5–3 gal/hour	~130–160 hours (~5–7 days)
Full load (22 kW)	~3.5–4 gal/hour	~100–115 hours (~4–5 days)

Those numbers are approximate — altitude, temperature, and the specific model all move them — but the shape is right: a 500-gallon tank gives you roughly 4 to 7 days of continuous running. If the outage lasts longer, or the roads are impassable for the delivery truck, you’re done.

The bottom line on availability: Natural gas wins for outages lasting up to a week in typical storm scenarios (no refueling needed, no tank to watch). Propane wins for true worst-case independence (no utility dependency at all), provided your tank is sized for your realistic outage duration and you keep it filled.

Practical rule: Whatever fuel you choose, size for your history. If your area’s worst outage in the last decade was 3 days, a 500-gallon propane tank is comfortable. If you’re in hurricane country where 2-week outages happen, propane gets expensive to size for (you’d want 1,000 gallons), and natural gas’s no-refill advantage grows.

Cost Comparison: Fuel, Installation, and Total Ownership

Fuel cost per kWh

This is where the math gets concrete. Let’s work through a typical example.

Assumptions:

Natural gas: $1.20 per therm (a therm = 100,000 BTU). US residential prices typically range from about $0.80 to $2.00+ per therm depending on the state — the Northeast and California run high, the Midwest and Texas run low.
Propane: $2.50 per gallon (a gallon of propane = ~91,500 BTU). Residential propane typically runs $2.00 to $3.50+ per gallon, varying by region, season, and whether you own or lease your tank.
Generator efficiency: a standby generator converts roughly 25–30% of fuel energy into electricity. We’ll use 28%.

Natural gas math:

1 therm = 100,000 BTU = ~29.3 kWh of heat energy
At 28% efficiency: 29.3 × 0.28 = ~8.2 kWh of electricity per therm
Cost: $1.20 ÷ 8.2 = ~$0.15 per kWh

Propane math:

1 gallon = 91,500 BTU = ~26.8 kWh of heat energy
At 28% efficiency: 26.8 × 0.28 = ~7.5 kWh of electricity per gallon
Cost: $2.50 ÷ 7.5 = ~$0.33 per kWh

So in this typical scenario, propane costs roughly twice as much per kWh as natural gas. That ratio holds across most US markets — propane is consistently the more expensive fuel to burn, usually by a factor of 1.8 to 2.5x.

What that means in dollars during an outage: A 22 kW generator running at half load for 24 hours produces about 264 kWh. On natural gas at $0.15/kWh, that’s roughly $40/day. On propane at $0.33/kWh, that’s roughly $87/day. Over a 5-day outage, the difference is about $235 — meaningful, but not the dominant cost compared to the generator itself.

There’s one more propane cost wrinkle: seasonal pricing. Propane prices spike in winter when heating demand peaks. If your outage happens during a cold snap — exactly when you’d be running the generator hardest — you’re refilling at the highest prices of the year. Natural gas prices are more stable month to month, though they vary by region.

Installation cost differences

Natural gas installation:

If your home already has natural gas service, the generator needs a dedicated gas line from the meter to the unit, sized for the generator’s full-load demand. A 22 kW unit needs roughly 250,000–300,000 BTU/hr at full load — that’s a substantial draw, and in many homes the existing gas meter and service line can’t handle the house load plus the generator simultaneously.
Meter upgrade: If your meter is too small, the utility upgrades it — typically $200–500, sometimes free depending on the utility.
Gas line run: A new dedicated line (usually 1” to 1¼” pipe depending on distance and load) trenched or run to the generator pad. For a typical 20–50 foot run, expect $500–1,500 from a licensed plumber or gas fitter. Long runs (100+ feet) can push $2,000–3,000+.
Total gas-side installation adder: roughly $700–2,000 on top of the generator and electrical work.

Propane installation:

The tank. A 500-gallon above-ground tank purchased outright costs roughly $1,500–2,500; a 1,000-gallon tank runs $2,500–4,000. Underground tanks cost more ($3,000–5,000+ installed) but solve aesthetic and some regulatory issues. Many propane companies offer leased tanks for $50–150/year, but leasing usually locks you into buying propane from that company — often at higher per-gallon prices.
Tank pad and setbacks. The tank needs a concrete pad or proper supports, and it must sit at specific distances from the house, property lines, and ignition sources per NFPA 58 (more on regulations below). Site prep and pad: $300–800.
Gas line from tank to generator: shorter than a typical natural gas run since you place the tank near the generator, but still requires a licensed installer. Expect $400–1,000.
First fill: 400 gallons at $2.50/gal = $1,000 sitting in your yard from day one.
Total propane-side installation adder: roughly $3,200–6,000+ for a purchased 500-gallon setup, or $1,000–2,000 with a leased tank (plus the ongoing lease and higher fuel prices).

The installation verdict: Natural gas is usually $2,000–4,000 cheaper to install if you already have gas service at the house. Propane’s tank is the big-ticket item. The gap narrows if you lease the tank, but then you pay more per gallon forever.

If you don’t have natural gas service at all — common in rural areas — extending a gas main to your property can cost $5,000–20,000+ or the utility may simply refuse. In that case propane wins by default; it’s the standard rural standby fuel for exactly this reason.

Performance Differences

Power output: propane has a slight edge

Here’s a detail buried in every spec sheet: standby generators produce slightly more power on propane than on natural gas. A Generac 22 kW unit, for example, is rated 22 kW on propane but about 19.5 kW on natural gas. Kohler and Cummins show the same pattern — typically a 10–12% derate on natural gas.

Why? Propane has higher energy density per unit of volume in the fuel-air mix the engine breathes. The engine can simply extract more power from each intake stroke on propane.

In practice, this matters at the margins. If your load calculation lands at 20 kW, the propane configuration handles it and the natural gas configuration doesn’t — you’d need to step up to the next model size (24 kW), which costs roughly $500–1,000 more. Size your generator on the fuel you’ll actually use.

Cold-weather performance

This is propane’s weak spot, and it matters in northern climates.

Propane boils (vaporizes) inside the tank at -44°F, which sounds like plenty of margin — but vaporization rate depends on temperature, tank size, and draw rate. The colder it gets, the slower liquid propane converts to vapor. Meanwhile, a 22 kW generator at full load is demanding a huge vapor flow.

The practical threshold: with a small tank (100–120 gallons) in sustained temperatures below about -20°F, the tank can’t vaporize fast enough to feed a large generator at high load. The generator starves, surges, or shuts down — during the coldest weather, when you need it most. Larger tanks (500+ gallons) have more liquid surface area and handle cold far better; the problem is worst with undersized tanks.

Natural gas doesn’t have this problem at all — pipeline gas arrives as vapor at whatever temperature, and cold weather doesn’t affect delivery (the Texas 2021 exception was a supply/production crisis, not a vaporization issue).

If you’re in USDA zone 5 or colder (regular sub-zero nights) and choosing propane, the fix is simple: don’t undersize the tank. A 500-gallon minimum for a 20+ kW unit, and consider 1,000 gallons if your design load is high. Some installers also specify a two-stage regulator setup, which handles pressure drop better in cold weather.

Maintenance and engine longevity

Both fuels burn cleaner than gasoline — no stale fuel, no carburetor gum, no ethanol problems. That’s one of the core advantages of a standby unit over a portable.

Between the two: natural gas burns slightly cleaner than propane, producing less carbon buildup on valves and pistons over thousands of hours. Propane is still very clean compared to gasoline or diesel. In residential service (typically 100–200 hours per year including weekly exercise cycles), the difference is negligible — both fuels will see the engine outlast the electronics. Neither fuel choice should drive your decision on maintenance grounds.

One genuine propane maintenance item: the regulator. Tank regulators last roughly 10–15 years and then need replacement ($150–300 installed). A failing regulator causes hard starting, surging, or shutdown under load — symptoms that mimic other problems. If your propane standby starts acting up after a decade, check the regulator’s age.

Shelf life and fuel stability

Neither fuel goes stale — a major advantage over gasoline portables. Natural gas is consumed as delivered; propane in a sealed tank is stable indefinitely. A propane tank filled today will be just as good in five years. This means no fuel stabilizer, no draining, no carburetor gum — ever.

Regulations, Setbacks, and HOA Realities

Propane tank placement is governed by NFPA 58 (the LP-Gas Code), adopted into law in most jurisdictions. Key rules for typical residential tanks:

Tank size	Minimum distance from house	Minimum from property line
125–500 gallons	10 feet	10 feet
500–1,200 gallons	10 feet	10 feet (with some exceptions)
Any size	10 feet from ignition sources (AC condensers, etc.)	—

Your local authority may add requirements — some municipalities require bollards (protective posts) if the tank is near a driveway, and fire marshals in wildfire zones may have additional clearance rules. Always check with your local building department before finalizing placement; the permit process will catch issues, but it’s cheaper to plan correctly first.

Underground propane tanks sidestep most aesthetic objections and some setback concerns, but they cost significantly more, require cathodic corrosion protection, and make future tank replacement a bigger project.

HOA restrictions are the wildcard. Some HOAs prohibit visible above-ground propane tanks outright; others require screening (fencing or landscaping). An underground tank usually satisfies even strict HOAs but doubles the tank cost. Natural gas has no visible equipment beyond the generator itself, so it’s the path of least resistance in HOA neighborhoods. Check your HOA covenants before you commit to propane — discovering the restriction after buying a $2,000 tank is an expensive surprise.

Natural gas permitting is simpler: the gas line work needs a permit and inspection like any plumbing work, and the generator needs its usual electrical permit. No fuel-storage regulations apply.

The Decision Framework

Forget “which fuel is better” — the right answer depends on your situation. Walk through these questions in order:

1. Do you have natural gas service at your house already?

No → Propane is your answer (or diesel, but that’s a different article). Extending a gas main is usually prohibitively expensive. Decision made.
Yes → Continue.

2. Can your gas service handle the generator’s load?

Have your installer do a gas load calculation: add up your furnace, water heater, stove, dryer, and the generator at full load, and check it against your meter’s capacity. If the meter needs an upgrade, that’s usually a minor cost ($200–500). If the service line from the street is undersized, costs climb — get a quote before deciding.

3. What’s your realistic worst-case outage?

Under a week, typical storms → Natural gas is the convenient, cheaper choice. No refueling, no tank monitoring.
Multi-week scenarios (hurricane coast, remote areas with slow utility restoration) → Propane’s independence matters more, but only if you size the tank honestly. A 500-gallon tank is ~5 days; size up or accept the limit.
Earthquake or flood zones → Propane. These are the scenarios where gas utilities shut down proactively.

4. What’s your winter climate?

Regular sub-zero temperatures + propane → budget for a 500-gallon minimum tank and confirm the regulator setup with your installer.
Any climate + natural gas → no cold-weather concerns.

5. HOA and property constraints?

Strict HOA or small lot where a 10-foot setback is hard to meet → natural gas avoids the fight entirely.
Acreage, no HOA → propane tank placement is trivial.

6. Budget structure?

Tight on upfront cost → natural gas (assuming existing service) is $2,000–4,000 cheaper to install.
Tight on running cost → natural gas again, roughly half the fuel cost per kWh.
Propane’s cost case is never “cheaper” — it’s “available where gas isn’t” and “independent of the utility.”

Quick-reference summary

Factor	Natural gas	Propane
Fuel cost per kWh	~$0.12–0.20 (typically)	~$0.25–0.40 (typically)
Installation adder (existing service)	$700–2,000	$3,200–6,000+ (purchased tank)
Outage refueling	Never needed	Tank lasts ~4–7 days (500 gal); delivery truck required
Utility dependence	Yes — rare interruptions possible	None — fully independent
Power output	~10–12% lower than propane rating	Full rated power
Cold weather	No issues	Vaporization limits below ~-20°F on small tanks
Fuel shelf life	N/A (pipeline)	Indefinite in tank
Visible equipment	Generator only	Generator + tank (HOA factor)
Best for	Suburban homes with gas service	Rural homes, quake/flood zones, no gas service

What About Dual-Fuel Standby Units?

Some standby generators can switch between natural gas and propane — either factory dual-fuel models or conversions. This sounds like the best of both worlds, and it can be: run on cheap natural gas normally, keep a propane tank as backup for the scenarios where gas service fails.

The reality check: you’re paying for both fuel infrastructures — the gas line work and the propane tank — plus the dual-fuel hardware premium (typically $500–1,500 over a single-fuel unit). And the propane tank still needs to be maintained, kept filled, and placed per code. For most homeowners, this is over-engineering. It makes sense in exactly one scenario: you have natural gas service, but you’re in an earthquake or flood zone where gas shutoff is a realistic risk, and multi-day outages are plausible. Otherwise, pick one fuel and size it right.

The Bottom Line

For the majority of suburban homeowners who already have natural gas service, natural gas is the right call: cheaper to install, roughly half the running cost, no refueling logistics, no tank to place or hide from the HOA. The power derate is real but easily handled by sizing the unit on its natural gas rating.

Propane is the right call when there’s no gas line to connect to (most rural properties), when you want full independence from utility infrastructure, or when your realistic disaster scenarios include the kind of events that take gas systems offline.

Either way, the fuel decision comes before the unit decision — size the generator on the fuel you’ll burn, get the gas work done by a licensed professional, and keep the tank filled (propane) or the meter adequate (natural gas). The best standby generator is the one that starts when the lights go out, and the fuel choice is what makes that happen.