Natural Gas vs. Propane Standby Generator — Which Fuel Fits Your St. Louis Home?
If a Spire natural gas main already runs to your St. Louis County street, natural gas is almost always the simpler and cheaper long-term choice — unlimited runtime, no tank to monitor. Propane is the right call when there's no gas main nearby, or you want fuel supply independent of any utility during an extended outage.
Fuel choice is one of the first decisions a contractor walks through before sizing your standby generator, and it affects more than the monthly fuel bill — it changes install cost, refueling logistics, and how the unit performs during a multi-day outage. Here's what actually differs between the two in a St. Louis County install.
Side-by-Side Comparison
| Factor | Natural Gas | Propane |
|---|---|---|
| Fuel supply | Continuous, piped from the Spire utility main | Finite, stored in an on-site tank |
| Runtime during an outage | Indefinite, as long as the gas grid stays pressurized | Limited to tank size — a 250-gal tank runs ~80-125 hrs at full load |
| Install requirement | Requires an existing or extendable gas main connection | Requires a propane tank and delivery contract |
| Energy density | Lower per cubic foot | Roughly double the BTU per cubic foot of natural gas |
| Best fit | Homes already on a gas main in denser St. Louis County suburbs | Rural lots or homes without gas main access |
Why Most St. Louis County Homes Default to Natural Gas
Natural gas and electric are separate delivery infrastructures, so a downed power line from an ice storm or derecho rarely takes the gas main with it. That's the core reliability argument for natural gas: your generator keeps running for the full duration of an extended outage without anyone needing to schedule a fuel delivery. It also skips the cost and yard space of a propane tank, and there's no risk of running dry mid-outage if a delivery truck can't reach your street.
Choose Natural Gas If
Your street already has a gas main, you want zero refueling logistics, and you're in a denser St. Louis County subdivision.
Choose Propane If
You're on a rural lot with no gas main nearby, or you specifically want fuel storage independent of any utility grid.
Once you know your fuel type, the next question is what size unit it needs to be — see our generator sizing guide. If a gas line needs to be run to the pad, our generator gas line install page covers what that work involves, and the whole-home generator page covers the full install scope either way.
Natural Gas vs. Propane FAQ
Is a natural gas or propane generator better for a St. Louis home?
Natural gas is usually the better fit if your street already has a Spire gas main, since it runs indefinitely without refueling and skips the propane tank entirely. Propane makes more sense on rural St. Louis County lots without a gas main, or where you want fuel stored independent of the utility grid.
Does a natural gas generator run at full power during an outage?
Yes, as long as the gas utility's distribution lines stay pressurized, which they typically do even when the electric grid is down, since gas and electric are separate infrastructure. That's the main reliability advantage natural gas has over stored propane.
How much propane does a whole-home standby generator use per hour?
A typical 16-22 kW standby generator burns roughly 2-3 gallons of propane per hour at full load, so a common 250-gallon residential tank provides somewhere around 80-125 hours of continuous full-load runtime before needing a refill.
Can a generator be converted from natural gas to propane later?
Many Generac and Kohler models support a factory conversion kit that swaps the fuel regulator and orifice, but it's not universal across every model year, so a contractor needs to check your specific unit before assuming a later switch is possible.
Codes & Standards
Fuel line and appliance tie-in work follows NFPA 70 (National Electrical Code) for the electrical side, and generator engine emissions on either fuel are governed by EPA stationary engine standards.