Fuel type is one of the first decisions you’ll make when buying a standby generator, and it affects everything from installation cost to how long you can run during an extended outage. Here’s how the three main options actually compare.
Quick Comparison
| Factor | Natural Gas | Propane | Diesel |
|---|---|---|---|
| Fuel supply | Continuous, piped from utility | Stored in tank, needs refilling | Stored in tank, needs refilling |
| Runtime limit | Unlimited (as long as gas service is active) | Limited to tank size | Limited to tank size |
| Upfront cost | Lower if gas line already exists nearby | Moderate — tank purchase/lease adds cost | Higher — diesel units and tanks cost more |
| Fuel cost over time | Generally cheapest per kWh | More expensive than natural gas per kWh | Most expensive per kWh in most regions |
| Shelf life of stored fuel | N/A (not stored) | Very long (years) with minimal degradation | Degrades over time, needs periodic treatment/rotation |
| Availability during widespread disaster | Can fail if gas infrastructure is damaged | Reliable if tank is full beforehand | Reliable if tank is full beforehand |
| Common home use | Most common choice when gas line is available | Common in rural areas without gas service | Less common for residential, more for commercial/large properties |
Natural Gas: Best for Uninterrupted Runtime
How it works: Connected directly to your home’s existing natural gas line (or a new line run to the generator), giving continuous fuel supply without needing to monitor a tank level.
Advantages:
- Truly unlimited runtime as long as the gas utility is functioning — no tank to run out
- Generally the lowest cost per kWh of the three options
- No need to schedule fuel deliveries or monitor tank levels
Disadvantages:
- Dependent on the gas utility infrastructure remaining functional — in a severe regional disaster that damages gas lines, this could theoretically be a single point of failure (though this is uncommon)
- Requires an existing gas line nearby, or the added cost of running a new one
Best for: Homeowners who already have natural gas service and want maximum runtime without the hassle of fuel management. This is why natural gas is the most common choice among the cost figures covered in our full breakdown.
Propane: Best for Fuel Independence
How it works: Stored in an on-property tank (owned or leased), which the generator draws from directly.
Advantages:
- Complete independence from utility gas infrastructure
- Propane has a very long shelf life, so a full tank can sit ready for extended periods without degrading
- Widely available in rural areas that may not have natural gas service at all
Disadvantages:
- Runtime is limited to tank size — you need to plan for how many days of outage you want to cover and size your tank accordingly
- Requires periodic refilling, and during widespread regional outages, propane delivery services can experience delays due to high demand
- Tank installation adds upfront cost and requires its own clearance/placement planning
Best for: Rural homeowners without natural gas access, or anyone who prioritizes fuel independence from utility infrastructure over unlimited runtime.
Diesel: Best for Heavy-Duty, Extended Use
How it works: Similar to propane in that it draws from an on-site tank, but diesel generators are more commonly found in larger commercial or agricultural applications than typical residential installations.
Advantages:
- Diesel engines are generally very durable and well-suited to running for extended periods under heavy load
- Diesel fuel is widely available, similar to gasoline
Disadvantages:
- Typically the highest upfront cost among the three for residential-scale units
- Stored diesel fuel degrades over time and needs periodic treatment or rotation to stay usable
- Diesel generators tend to be louder and require more maintenance attention than natural gas or propane equivalents
Best for: Larger properties or homeowners with existing diesel infrastructure (like a farm with diesel equipment already), rather than a typical suburban home.
How to Decide
The most practical starting point is simple: do you already have a natural gas line to your home? If yes, it’s usually the default choice unless you have a specific reason to prioritize fuel independence. If no natural gas service is available, the choice becomes primarily between propane (more common for residential) and diesel (more common for larger or commercial-adjacent properties).
Frequently Asked Questions
Can a generator run on more than one fuel type? Yes — dual-fuel generators exist that can switch between natural gas and propane, offering some flexibility, though they’re less common than single-fuel units and typically cost more.
Does fuel type affect the transfer switch or installation process? The transfer switch itself works the same regardless of fuel type, but propane and diesel installations add a tank installation step that natural gas doesn’t require.
Which fuel type is cheapest to run long-term? Natural gas is generally the cheapest per kWh in most U.S. regions, though local utility rates vary enough that it’s worth comparing your specific area’s natural gas and propane pricing.
Bottom Line
Natural gas offers unlimited runtime and the lowest running cost if you already have service; propane offers fuel independence with a limited but plannable runtime; diesel is generally better suited to larger or commercial-adjacent properties than typical residential use. For most homeowners with gas service already available, natural gas is the simplest and most cost-effective choice.