Around here, the honest first answer is: your address probably already chose. In-city Huntsville and Madison sit on natural gas mains; Harvest, New Market, Hazel Green, and rural Limestone County don’t, and run propane. Where you genuinely have both options — newer developments, the growth corridors, split-fuel Athens — the decision comes down to supply continuity versus on-site independence, plus a cost structure we’ll lay out plainly. This is one of two pages on this site that crosses from generator sizing and fuel supply into cost territory, because the fuels genuinely differ there.
What’s the fundamental difference between the two fuels?
Continuity versus custody.
Natural gas arrives continuously from the utility main. Your generator can run for as long as the outage lasts without anyone thinking about fuel — the supply is effectively unlimited, metered as used. The constraint sits at the meter, which caps flow, not duration.
Propane is yours, on-site, in a tank. Nothing upstream can fail, no utility is involved — and the supply is finite. The constraint is tank sizing and the runtime math, gallons against burn rate, with refill trucks as the resupply plan.
Same generator either way, near enough: home standby units run on either gaseous fuel, configured at install, with slightly different output ratings per fuel on the spec sheet because propane carries more energy per cubic foot.
Which fuel wins on outage reliability?
Both, in different failure modes — and it’s worth being precise, because this is where sales pitches get loose.
Gas mains keep flowing through nearly every power outage; the electric grid and the gas network fail independently, which is the whole premise of a gas-fed standby unit. But “nearly” is honest: severe ground-disturbance events can interrupt gas service, and when that happens there’s no local reserve.
Propane can’t be interrupted upstream because there is no upstream — the trade is that a multi-week event tests your tank size, and post-storm refill queues in the county are real. If your planning scenario is the 2011 kind of week, gas answers with indefinite runtime and propane answers with whatever you stored ahead of time.
How do the costs compare — structurally?
We don’t post specific dollar rates here — gas and propane prices move seasonally and vary by supplier. The structure, though, is worth knowing and doesn’t change.
Operating cost: natural gas is billed per therm as consumed; propane is bought by the tank-fill ahead of need, at per-gallon prices that move seasonally and independently of gas rates. Install cost: fuel choice changes exactly one of the seven invoice line items — the fuel connection. A gas-fed install runs a line from the meter (possibly upgrading it); a propane install adds tank siting, the tank itself or a lease, and trenching if buried. The other six line items don’t care which fuel you burn — the installed-cost breakdown walks all seven.
So which one should your generator run on?
If you’re in the city on a main: natural gas, almost always — indefinite runtime is the killer feature, and the only real gate is whether your meter can feed the unit you want. If you’re in the county: propane, by necessity, sized honestly for the outages you’re planning around. If you’re on the edge with both available: gas for set-and-forget continuity, propane for independence from shared infrastructure — and either way, the tier you pick interacts with the fuel more than any brochure admits.