The Short Answer: Natural Gas vs Propane

Natural gas is the preferred fuel for most homeowners who have access to a municipal gas line. It provides an unlimited fuel supply, lower operating costs, and eliminates the need for on-site fuel storage. Propane is the best choice for rural homes without natural gas service, or for homeowners who want fuel independence from the utility grid.

Side-by-Side Comparison

Factor	Natural Gas	Propane
Fuel supply	Unlimited (utility line)	Limited to tank size
Runtime	Indefinite	Days to weeks (tank-dependent)
Fuel cost	$0.80–$1.20/therm	$2.50–$4.00/gallon
Operating cost (20kW)	$2–$4/hour	$3–$6/hour
Power output	Full rated output	5–10% less than NG
Storage required	None	250–1,000 gallon tank
Tank installation cost	N/A	$800–$2,500
Fuel availability in outage	Usually maintained	Stored on-site (independent)
Cold weather performance	Excellent	Reduced below -44°F
Rural availability	Limited	Available everywhere

Natural Gas: Advantages and Limitations

The primary advantage of natural gas is its unlimited fuel supply. As long as the gas utility maintains service — which is the case in the vast majority of outages, including most hurricanes and winter storms — your generator will run indefinitely without any action on your part. This is the key reason most homeowners with gas line access choose natural gas.

Natural gas also burns cleaner than propane, producing slightly lower emissions and requiring less frequent spark plug replacement. Operating costs are typically 30–50% lower than propane at current fuel prices.

The limitation of natural gas is its dependence on the utility infrastructure. In rare but serious events — the 2021 Texas winter storm being the most notable example — natural gas supply can be disrupted. For homeowners in areas with known gas supply vulnerabilities, propane provides an important layer of resilience.

Propane: Advantages and Limitations

Propane's key advantage is fuel independence. A 500-gallon propane tank provides approximately 7–10 days of continuous operation for a 20 kW generator. A 1,000-gallon tank extends this to 14–20 days — more than enough for any realistic outage scenario. For rural homeowners without natural gas service, propane is the only practical standby generator fuel option.

Propane also has a longer shelf life than gasoline (indefinite when stored properly in a sealed tank), making it superior to portable gasoline generators for emergency preparedness.

The limitations of propane include higher operating costs, the need for on-site tank installation ($800–$2,500), ongoing propane delivery logistics, and slightly reduced power output compared to natural gas. Propane also becomes less reliable in extreme cold — below -44°F, propane will not vaporize properly, though this temperature is rarely reached in most of the US.

How Much Propane Does a Standby Generator Use?

Generator Size	Propane Use (50% load)	500-gal Tank Runtime	1,000-gal Tank Runtime
14 kW	1.2 gal/hr	~17 days	~34 days
20 kW	1.6 gal/hr	~13 days	~26 days
22 kW	1.8 gal/hr	~12 days	~23 days
26 kW	2.1 gal/hr	~10 days	~20 days

Dual-Fuel Generators: The Best of Both Worlds

Some Generac models offer dual-fuel capability, allowing the generator to run on either natural gas or propane. This provides the convenience of natural gas for everyday use with propane as a backup if gas service is disrupted. Kohler does not currently offer a dual-fuel residential standby generator. If fuel resilience is a priority, Generac's dual-fuel lineup is worth considering.

Which Fuel is Right for Your Home?

Choose natural gas if: You have a gas line to your home, you want the lowest operating cost, and you prefer a fully automatic system with no fuel management required.

Choose propane if: You do not have natural gas service, you live in an area with known gas supply vulnerabilities (rural Texas, areas prone to severe winter storms), or you want complete fuel independence from the utility grid.

Frequently Asked Questions

Is propane or natural gas cheaper for a generator?

Natural gas is typically 30–50% cheaper per hour of operation than propane at current fuel prices. A 20 kW generator costs approximately $2–$4/hour on natural gas versus $3–$6/hour on propane.

Can I convert a natural gas generator to propane?

Yes, most Kohler and Generac standby generators can be converted between natural gas and propane by a certified technician. The conversion requires a different carburetor jet and regulator. Cost is typically $200–$500 in parts and labor.

How big of a propane tank do I need for a whole home generator?

A 500-gallon tank is the minimum recommended for a 20–22 kW generator, providing 10–13 days of runtime at typical loads. A 1,000-gallon tank is recommended for larger generators or homeowners who want extended runtime during prolonged outages.