Florida generator guide

The '50% Load' Fuel Myth: Why the Generator Spec Sheet Misleads You

Line up two spec sheets. Both promise a tidy number for fuel burn "at 50% load." One's a 10kW unit, the other's a 26kW. Same phrase, same confident little figure — and they're describing two completely different amounts of your house. So which one tells you what your next outage will actually cost you? Honestly, neither. Here's why that number fools almost everyone.

Get your address-specific installed price →

About five minutes. No salesman, no all-day window.

Same words, two different houses

Fifty percent sounds like it means something fixed. It doesn't. Half of a 10kW generator is five kilowatts of your home running. Half of a 26kW is thirteen. That's not a small gap — that's the difference between keeping the fridge, some lights, and one window unit alive versus running the whole downstairs plus central air.

So when a chart lists both units' fuel burn "at 50% load" side by side, it's quietly measuring two totally different jobs and printing them in the same column. It's like being told a vehicle "sips fuel at half throttle" without anyone mentioning whether it's a scooter or a dump truck. Half throttle on one of those is a very different afternoon than the other.

The percentage is a slice of the nameplate. And the nameplates aren't the same size. That's the whole trick.

Half the load isn't half the fuel

Here's the part that surprises people. You'd think dropping a generator from full power to half would cut the fuel bill in half too. It doesn't.

An engine burns fuel just to exist — turning itself over, staying at speed, keeping cool, running the parts that make the electricity. Those costs don't shrink when you ask for less power. So a unit sitting at 50% load usually burns somewhere around 60 to 70 percent of its full-throttle fuel rate, not 50. The math you assumed was hiding in that clean little number was never there.

Which means even the relationship between the '50%' line and the '100%' line on the same spec sheet isn't what your gut tells you. The number looks precise. It's just precise about the wrong thing.

The only number that matters is what your house pulls

Walk past both generators for a second and look at the house. Your refrigerator draws what it draws. Your air handler, your well pump, your pool equipment — they need a certain number of watts to run, and that number does not care which generator is bolted to the slab outside.

So the real fuel question isn't "what's 50% of the generator." It's "how many kilowatts is my house actually going to pull during the storm." Put a giant generator on a modest load and it just runs at a smaller slice of its rating — same house, bigger engine idling along, often burning more than the job needed. One homeowner with a unit rated for about three and a half gallons an hour found it only sipped roughly a gallon and change during a real outage, because nobody runs the whole house flat-out at 3 a.m. The spec sheet described a moment that almost never happens.

That's the assumption worth breaking before you buy: bigger is not automatically safer on fuel. An oversized unit spends most of an outage lightly loaded, which wastes propane and, over years, isn't kind to the engine either. The right size is the one matched to what your specific home actually draws — not the biggest one on the shelf.

So what will it actually cost at your house?

Notice what a spec sheet can't tell you. It doesn't know your square footage, your AC tonnage, whether you're on natural gas or a propane tank in the side yard, or how much you'd really run during a week without power in August. It just prints a percentage and lets you do the guessing.

GENERasic does the opposite. Instead of handing you a fuel chart and a shrug, we size to the load your home actually pulls and give you one committed installed price for your exact address — not a range, not a "starting at," not a number that changes after someone walks your property. The kilowatts your house needs decide the unit; the unit decides the fuel; and you see the real out-the-door figure up front.

Skip the spec-sheet arithmetic. Get your price for your address and find out what powering your home actually takes.

Common questions

If I don't know my home's load, how am I even supposed to calculate fuel use?

You mostly can't from a spec sheet, and that's exactly the problem — a fuel number is meaningless until you know how many kilowatts your house pulls. That depends on your AC, well pump, water heater, and what you run at once. It's why matching the generator to your actual load comes first; the fuel figure falls out of that, not the other way around. When we price your address, sizing to your real load is step one.

Will a bigger generator just cost me way more in fuel?

Often, yes — and not because it's doing more work. Your house pulls the same watts no matter how big the unit is, so an oversized generator spends most of an outage lightly loaded, running at a smaller slice of its rating and burning fuel it didn't need to. Light-loading like that also isn't great for the engine long term. The efficient choice is the unit sized to what your home actually draws.

My generator is rated for around 3.5 gallons an hour — will it really burn that?

Almost certainly not for most of an outage. That rating is the full-throttle, everything-on number, and homes rarely run flat-out. Real-world reports from homeowners during actual outages often land closer to a third of the rated burn, because the unit cycles up and down with whatever's running inside. The rated figure is a ceiling, not a forecast.

How long will my propane tank last during an outage?

It depends far more on your real load than on the tank sticker. As a rough feel, a 250-gallon tank tends to carry a typical home several days of real-world use, and a 500-gallon tank can stretch to a week or more, because you're rarely at full load. Natural gas sidesteps the tank question entirely, as long as the line stays pressurized. The honest answer comes from your actual draw, which is what we size to.

Does the 50% number change if I'm on natural gas instead of propane?

The fuel type changes the units and the cost, but not the core problem: a percentage of the nameplate still doesn't tell you what your house pulls. Natural gas is usually billed by the cubic foot and often runs a bit cheaper per hour than propane, while propane has the advantage of not depending on a gas line staying live during a storm. Either way, the load your home actually draws is what drives the burn — not the percentage on the chart.

Stop reading ranges. Get your number.

GENERasic pulls the real property, flood, and elevation data for your exact address and returns one all-in installed price — sized to your home, your fuel, and your flood elevation. The vetted local installer confirms it on site.

Get your installed price →