How long a generator runs on propane

Every standby generator spec sheet lists fuel use at set loads. Generac publishes two points for its air-cooled Guardian units: half load and full load. That is all you need for honest planning.

The 26 kW Guardian, the default example on this site, burns 2.06 gallons of propane an hour at half load and 3.63 gallons an hour at full load, per Generac's spec sheet (Rev. D, September 2022). The 22 and 24 kW Guardian units burn 2.53 gallons an hour at half load and 3.90 at full load.

The second number you need is usable fuel. Propane tanks are filled to about 80 percent of their water capacity, never full, because liquid propane expands as it warms. Ferrellgas lists the usable amounts:

• 120-gallon tank: about 96 gallons
• 250-gallon tank: about 200 gallons
• 500-gallon tank: about 400 gallons

Divide usable gallons by gallons per hour and you have runtime from full to empty, running around the clock:

• 120 gallons: about 47 hours, roughly 1.9 days, on the 26 kW at half load. About 38 hours on a 22 or 24 kW unit.
• 250 gallons: about 97 hours, roughly 4.0 days.
• 500 gallons: about 194 hours, roughly 8.1 days.

At full load, the 26 kW burns about 87 gallons a day, so a 120-gallon tank lasts a little over a day.

Two cautions. Real load swings through the day, so treat half load as a planning point, not a promise. And many people prefer not to run a tank below about 20 percent; held to 80 to 20 percent, a 500-gallon tank gives about 6.1 days on the 26 kW. Your installer works out the numbers for your actual loads.

Run the runtime numbers for your unit before you choose a tank

This is the local fact most generator pages leave out. The district ARC manuals, posted on districtgov.org and checked on October 28, 2026, allow underground or aboveground propane tanks. An aboveground tank needs approval and is limited to one tank of no more than 120 gallons. The manuals state no size limit for a buried tank. Tanks must stay out of view of the road and neighbors and out of utility easements.

A full 120-gallon tank runs a 26 kW unit about 1.9 days at half load. Milton's local outages took about four days to clear. So a propane home on an above-ground tank has a gap to close, and there are five honest ways to close it:

1. Natural gas, where a main reaches the home. No tank to run dry. See natural gas in The Villages.
2. Load management. Running nearer half load than full load makes a tank last about 75 percent longer. More below.
3. Right-sizing. A smaller unit sized for essentials can burn less fuel at the same share of its rating. Check its own spec sheet; Generac lists its 18 kW at 1.70 gallons an hour at half load.
4. A larger buried tank, if it fits. About 4.0 days on 250 gallons and 8.1 days on 500 at half load. NFPA 58 setbacks and easements rule one out on many small lots, so the installer and the ARC confirm what fits.
5. A refill plan. A delivery booked early in the outage, not on the last morning.

None of this is a reason to skip a generator. Two days of air conditioning, refrigeration and oxygen covers most outages on its own, and a refill plan covers the rest. It is a reason to plan with real numbers. The propane tank limits page covers the tank rules and placement, and natural gas vs propane compares the two fuels in full.

Ask your installer which tank rule your district manual sets

Where a natural gas main reaches the house, the generator draws fuel from the utility line. The Generac 26 kW uses 188 cubic feet an hour at half load and 333 at full load. At half load that is about 4,512 cubic feet a day. There is no tank to measure and no truck to wait for, which is why natural gas is the strongest single choice for a long outage.

A few facts keep the picture honest:

• The meter has to keep up. A 24 to 26 kW unit at full load draws 290 to 333 cubic feet an hour on top of the furnace, water heater and range. Peoples Gas asks customers and installers to report standby generators, and its form asks whether a Peoples Gas technician has checked the meter and regulator size.
• The gas utility varies by address. Peoples Gas serves much of the community, but a 2020 PSC filing shows The Villages and the City of Leesburg planned for Leesburg to serve future developments in Sumter County. Your installer confirms which utility serves you.
• Buried pipe held up well in 2024. Peoples Gas says fewer than 1 percent of its more than 500,000 customers had a gas interruption in the 2024 storms. That is the company's own figure.
• Supply can still be stressed. In Winter Storm Uri in 2021, the FERC and NERC report found natural gas supply problems in 87 percent of fuel-related power plant failures in Texas. During Hurricane Ida in 2021, DOE reported about 86 percent of federal Gulf of Mexico gas production shut in. Neither event happened here, and neither predicts Florida, but they explain why no fuel is promised forever.

Pipe size matters too. Generac says to size the fuel supply for full load, using the pipe tables in each model's installation manual. Your installer and the gas utility handle that part.

Have your installer confirm meter size with your gas utility

A generator burns propane as a vapor, not a liquid. The tank boils liquid into vapor using heat from the air or soil around it. The Propane Education and Research Council (PERC) explains that vapor output depends on how much of the tank's surface is wet with liquid, how full it is, the air temperature and humidity, and whether the tank is above or below ground. Less liquid or colder air means less vapor.

PERC's own table is conservative and stops at 40 F, far colder than a Villages hurricane season. Using its rule for continuous loading at 40 F, even a 500-gallon tank falls short of a 22 to 26 kW unit at half load. Real performance in Florida heat is better, and buried tanks benefit from steadier soil temperatures, but PERC publishes no figure above 40 F. What this means for you is practical:

• A small tank that is nearly empty delivers less vapor than the same tank when full. Do not plan to run a 120-gallon tank to the last gallon.
• Your installer should size the tank and regulators for vapor delivery at full load, not just for gallons stored.
• A secondary regulator near the generator drops tank pressure to the inlet range on the spec sheet. Generac lists 10 to 12 inches of water column for propane.

Placement rules for propane tanks come from NFPA 58 as adopted locally, plus the ARC manual for your district. Distances from the house, windows, air conditioners and property lines differ by tank size and by whether the tank is buried. Your installer and the propane supplier confirm the setbacks for your lot.

The courtyard villa page covers the tight side yards where these rules matter most.

Ask for a tank and regulator sized for full-load vapor, not just gallons

A propane tank is only as long-lasting as your next delivery. Florida's storm history shows why to book it early.

After Irma in 2017, the Florida Propane Gas Association told Butane-Propane News that the state had limited propane storage, many bulk plants had no power to pump propane out, and with rail and ports down, trucks were the only way to bring propane into Florida for about seven days. The state prioritized propane for backup generators, emergency kitchens and critical facilities. Gasoline was tight too: GasBuddy data showed about 43 percent of Florida gas stations out of fuel on September 12, 2017. The EIA notes Florida has no refineries and depends on marine shipments through its ports.

A refill plan for a propane home looks like this:

1. Know your supplier. Write the company name, account number and phone number on paper, not only in your phone.
2. Top off before the season and again when a storm is forecast. Starting at 80 percent instead of 50 percent is the cheapest runtime you will ever buy.
3. Read the gauge every morning during an outage, when you check the oil.
4. Call for delivery early. At about half a tank, not at empty.
5. Keep the path clear. PERC advises that tanks be accessible to the delivery truck. Make sure gates, carts and debris do not block the fill point.

None of this replaces asking your supplier how it handles storm priority. Ask before the season, and write the answer down. The long-term preparedness plan puts the refill step alongside water, food and oil.

Write your propane supplier's number on the readiness shelf today

The single biggest lever on runtime is load. The 26 kW Generac burns 2.06 gallons an hour at half load and 3.63 at full load. Keep the house nearer half load and the same tank lasts about 75 percent longer than it would at full load.

Modern standby systems do much of this automatically:

• Generac's service-rated transfer switch on the 26 kW can manage up to four air conditioning loads with no added hardware, and its Smart Management Modules can shed up to eight more large 240-volt loads, adding them back when the generator has room.
• Kohler's load management can handle up to six residential loads by priority.
• Cummins lists control of up to four loads on its RS20A.

You can stretch fuel by hand as well:

• Set the thermostat a few degrees higher than usual and close off rooms you are not using.
• Run the dryer, oven and dishwasher one at a time, in the cooler hours.
• Skip the pool pump and any second refrigerator in the garage.
• Keep the main refrigerator, freezer, medical equipment and one cooling zone as the priorities.

Generac also asks for a shutdown of at least 30 minutes after every 24 hours of continuous running to check oil. That short pause stretches calendar time a little too.

A smaller, well-managed unit is often the better long-outage machine than a big one running near full load. The sizing guide helps you find the balance, and the AC page shows how to keep cooling on the list without blowing the budget.

Request a free estimate with load management priced in