Natural Gas vs Propane Generator

For a permanently installed standby generator, this is usually the choice. Both are clean-burning gaseous fuels with indefinite storage life. The difference is where the fuel comes from.

Natural gas

Piped from the utility, metered like your other gas appliances.

Advantages:

• Effectively unlimited runtime. No tank to empty, no refuelling, no delivery to arrange
• Usually cheapest per unit of energy
• No storage — nothing in your yard, no tank aesthetics or setbacks
• Nothing to run out of during an extended outage

Disadvantages:

• Lowest output of the three common fuels
• Requires gas service, which many rural properties don't have
• Depends on the utility. Usually reliable, not guaranteed
• Meter and line sizing must support the generator's demand — a real installation issue

Propane

Stored on site in a tank you own or lease.

Advantages:

• More output than natural gas
• Independent of utilities. Nothing to interrupt except your own supply
• Available anywhere, including rural properties with no gas service
• Stores indefinitely — no degradation, no stabilizer
• You control the reserve. Fill the tank before storm season

Disadvantages:

• Finite. It runs out, and refilling during a widespread emergency can be slow
• Usually costs more per unit of energy than natural gas
• A tank in the yard, with placement rules and setbacks
• Cold-weather vaporization — output falls in deep cold with a low tank

Side by side

The output penalty

Both produce less than gasoline, and the gap matters when sizing.

A generator rated 22 kW on propane might be around 19–20 kW on natural gas. Manufacturers publish both figures for dual-fuel-capable standby units.

Size against the fuel you'll actually run. Using the higher rating when you'll run the lower fuel means quietly buying a smaller generator than you think. See what can a generator run.

Does gas keep flowing in an outage?

Usually yes, and it's the main argument for natural gas in standby applications.

Gas distribution is largely pressure-driven and generally continues during electrical outages. That's why standby generators favor it: unlimited fuel, delivered automatically, during exactly the event you bought the generator for.

It isn't guaranteed. Earthquakes, major infrastructure damage, and service work can interrupt supply. In seismic regions this is a real consideration, and it's part of why some homeowners choose propane despite the extra cost.

Meter and line sizing

An installation detail that catches people out.

A standby generator is a large gas load — often comparable to or exceeding all your other gas appliances combined. Your existing meter and gas line may not have the capacity.

Consequences:

• The utility may need to upsize the meter
• The installer may need to run a larger gas line from the meter to the generator
• Both take time and add cost, and utility scheduling can dominate the timeline

Ask about this early. It's a common source of both delay and unexpected cost — see standby generator installation cost.

Propane tank sizing

Small cylinders are unsuitable for standby use — a 20 lb BBQ cylinder is measured in hours, not days.

Residential standby installations typically use tanks in the hundreds of gallons, so that several days of runtime are available without a delivery. Tanks can be owned or leased, and leasing usually ties you to one supplier.

Placement is regulated — setbacks from buildings, property lines, and ignition sources. See propane tank sizing for a generator.

Cold weather

Propane vaporizes less readily as temperature falls, and vapor pressure drops further as the tank empties. A large tank has more surface area for vaporization, which is one reason standby installations use big tanks rather than several small ones.

In severe cold with a low tank, a generator can starve for fuel — exactly during a winter storm.

Natural gas doesn't have this problem.

Choosing

Natural gas, if: you have gas service with adequate capacity, you want unlimited runtime with zero attention, and you're not in a region where seismic interruption is a live concern.

Propane, if: you have no gas service, you want independence from utilities, you need the extra output, or you want a reserve you control and can top up before a storm.

Dual-fuel standby units exist and can run either, which is worth asking about — the flexibility costs little and covers both failure modes.

Where to go next

• Propane tank sizing for a generator
• Generator fuel types
• Standby generator installation cost
• Size it properly: generator sizing calculator

More in our generator and backup power guides.