It’s the question almost every Lowcountry homeowner asks before buying: if a hurricane knocks out Dominion Energy South Carolina for three or four days, will my generator actually last that long? The honest answer depends almost entirely on one thing, what you’re feeding it. Natural gas and propane behave very differently over a long outage, and understanding the difference up front is how you avoid a nasty surprise on day two of no power.
A quick note. Lowcountry Generator Pros connects you with a single vetted, licensed local installer who handles sizing, permitting, and the install. We’re a homeowner resource, not the contractor, and we don’t publish reviews or ratings, our job is to help you understand the trade-offs before you talk to anyone.
Natural gas: effectively unlimited
If your home runs the generator off a natural-gas line, which many Charleston-metro homes can, since Dominion supplies gas across much of the area, runtime is essentially a non-issue. The generator pulls fuel continuously from the same utility line that feeds your range and water heater, and that line keeps flowing independently of the electrical grid.
So during a multi-day outage, a natural-gas standby unit can run for days on end without anyone refueling anything. There’s no tank to watch, no gauge dropping, no trip to arrange. The practical limit isn’t fuel, it’s the maintenance the engine needs on very long runs, which we’ll get to below. For most people, “how long will it run?” on natural gas comes down to “as long as the outage lasts.” This is a big part of why gas is the default recommendation where it’s available; see natural gas vs. propane for the full comparison.
Propane: tank-size math
Propane changes the equation because you’re running off a finite supply sitting on your property. The generator will run cleanly for as long as there’s fuel in the tank, but that tank empties, and how fast depends on the size of the unit and how hard it’s working.
The rough way to think about it: a generator’s propane consumption is usually given in gallons per hour at partial and full load. Multiply that burn rate by the hours you expect to run, and you have your fuel demand. Then compare it to your usable tank capacity, and note that propane tanks are only filled to about 80% for safety, so a “500-gallon” tank holds closer to 400 usable gallons.
A worked-through example makes it concrete. Suppose your unit burns roughly 2 to 3 gallons per hour under a typical household load. Over a full 24-hour day that’s somewhere around 50 to 70 gallons. Against ~400 usable gallons in a 500-gallon tank, you’re looking at a handful of days of runtime, often enough to cover a typical Lowcountry storm outage, but not indefinite. Actual burn rates vary by unit and load, so treat these as planning figures, not a promise; your installer will run the real numbers for your specific generator and tank.
Sizing the tank for a multi-day outage
Here’s where the tank decision matters. The Lowcountry doesn’t get short, tidy outages, after storms like Matthew and Irma, and famously after Hugo, power stayed out for days across Charleston, Berkeley, and Dorchester counties. If you’re on propane, you want a tank sized for that reality, not for a two-hour blip.
That usually means going bigger than you’d first guess. A homeowner planning around a realistic three-to-five-day outage window, plus a margin, because refills can be hard to get right after a storm, often lands on a larger tank than a quick calculation suggests. This is exactly the kind of trade-off to settle during sizing; our how to size a home standby generator guide covers matching the unit and fuel supply to how your household actually uses power.
Plan your refills before the storm, not during
The catch with propane is that the moment you most need a refill, mid-outage, right after a hurricane, is also the moment refills are hardest to get. Roads flood, suppliers are slammed, and delivery trucks are backed up across the region. That means propane runtime is really a two-part plan:
- Top off before hurricane season, and top off again when a storm is forecast. Going into an outage with a full tank buys you the most runtime with zero logistics.
- Know your supplier’s storm policy. Some prioritize existing standby-generator customers; ask before you need to.
- Don’t count on a mid-storm refill. Size the tank so you’d be fine even if no truck arrives for several days.
Natural-gas homes skip all of this, which is one more reason gas wins where it’s available. In neighborhoods without gas service, more common on the rural fringes and out toward Goose Creek and the Berkeley County edges, propane with a well-sized tank is the proven path.
Oil and maintenance on long runs
There’s one runtime limit that applies no matter the fuel: the engine. A standby generator running continuously for days is doing far more work than its weekly self-test. On extended runs, the engine oil is being used the whole time, and manufacturers specify oil-change and check intervals based on run hours, not just calendar months.
For a genuinely long outage, that can mean a mid-outage oil and filter check to keep the unit healthy, something to plan for rather than discover. Keeping up with routine service between storms also means the machine is in shape to handle a marathon run when one comes. Our generator maintenance guide lays out the self-test, oil, and pre-season checklist that keep a unit storm-ready.
The bottom line
On natural gas, runtime is effectively unlimited, you’re capped by engine maintenance on very long outages, not by fuel. On propane, runtime is a math problem: tank size versus burn rate, planned around a multi-day outage and topped off before the storm. Either way, a properly sized standby system is built to carry a Lowcountry home through the kind of extended outage this coast actually gets.
To figure out which fuel and what runtime make sense for your home, start here and we’ll connect you with a vetted local installer, or read will a standby generator run through a hurricane? for how all of this holds up in a real storm.