Fuel supply, not wattage, determines whether the lights stay on during day four of an outage. A propane tank runs until the liquid hits the bottom, then someone must schedule a refill — often when every truck in the county is booked. That single difference decides most home backup setups in the U.S.
Natural Gas vs Propane Generator: What Actually Decides The Answer
The deciding factor is existing fuel infrastructure, not brand or price. If a gas meter already sits against the house, natural gas is simpler and usually cheaper per hour. If the nearest gas main is a quarter mile away, propane wins by default because it arrives on a truck.
- Natural gas: feeds from the utility line, no refueling logistics, no tank to monitor — but stops the moment utility gas stops.
- Propane: stored onsite, fully independent of utility gas, delivers slightly more output per the same engine.
- Neither wins on convenience alone: a gas line that fails during a regional disaster takes the generator down with it.
A gas line that doesn’t exist costs thousands to bring to the property; a propane tank that doesn’t exist costs a tank, a pad, and a delivery contract. Either way, the fuel decision is a site decision.
Output, Cost, And Runtime Differences That Matter
Propane produces more kilowatts from the same generator — the gap shows in Generac’s own listings. The Next Gen 22kW air-cooled model is rated 22 kW on liquid propane but 21 kW on natural gas. The Next Gen 24kW unit is rated 24 kW on propane and 22.5 kW on natural gas. Those reflect the lower energy density of utility gas.
Skipping that gap is a common ordering mistake. A homeowner sizing for a 20 kW load on natural gas may find the unit only delivers about 17 kW — and the air conditioner or well pump won’t start. Size against the fuel’s actual rating, not the badge.
Runtime diverges most. A propane generator’s runtime is limited by tank size, and a typical 500-gallon tank might carry a whole-home unit for days, not weeks, depending on load. That’s fine for a 24-to-48-hour outage; a real problem during a week-long regional event.
Dual-Fuel Generators Solve The Wrong Problem For Most Homes
Generac’s home standby units are field-selectable for natural gas or liquid propane at install — the same generator runs on either fuel depending on what’s plumbed to it. That flexibility sounds like a perfect hedge, but it’s usually a one-time choice. Once the installer connects one fuel, that’s the fuel.
Still, dual-fuel capability is useful during the buying stage: a homeowner moving, or planning to add propane later, isn’t locked into a one-fuel generator.
A dual-fuel model is the safer buy when the fuel source isn’t confirmed. For readers comparing models by output and price, the tested gas backup generator roundup breaks down which wattage actually covers a typical home load.
The Bottom Line: Match The Fuel To The Property
- Has a gas meter and wants zero refueling hassle: natural gas. Cheaper per hour, unlimited runtime, no tank to monitor.
- No gas service, or wants independence from utility infrastructure: propane. Onsite storage, higher output per unit, no dependency on a gas main that could fail.
- Wants a long outage hedge and has no gas line: propane with an oversized tank, sized against actual load.
- Fuel source still undecided: a Generac dual-fuel standby, selected at install once the fuel plan is final.
Generac’s product documentation lists these units as auto-start after an outage, with fuel selected at installation, and the field manuals note the same engine can operate on either LPG or natural gas depending on setup. The fuel choice is made once.
Avoid comparing generators by wattage alone. Two units rated identically on propane can produce meaningfully different output on natural gas — and that difference shuts off the air conditioner during a heat-wave outage. Price the fuel, size against the correct fuel rating, and the generator will do its job.
FAQs
Does a natural gas generator keep running during a power outage?
Yes, as long as the utility still supplies gas. It pulls fuel from the same meter that feeds the house, so it doesn’t need refueling. The catch: widespread utility gas interruptions — rare, but real during regional disasters — will shut the generator down along with everything else.
How long will a propane generator run on a full tank?
It depends on tank size and load. A 500-gallon tank may carry a whole-home generator for several days under moderate load, but a larger unit running hard in summer heat will burn through it faster. For outages that frequently stretch past a few days, an oversized tank is worth the extra cost.
Can a Generac standby generator run on both fuels?
Once the installer connects one fuel source, that’s the fuel the generator uses going forward.
References & Sources
- Generac. “9500-Watt Tri Fuel Electric Start Portable Generator.” Confirms Generac’s tri-fuel and dual-fuel fuel-selection capability and current product listings.
- Generac. “Air-Cooled Standby Generator Installation Manual.” Documents LPG/NG fuel compatibility and installation fuel-selection requirements.
