Florida generator guide

How Long Will My Propane Tank Actually Run My Generator?

The storm's already here, you're out by the tank with a flashlight, and you're trying to do long division in your head while the wind works on the neighbor's pool screen. Here's the short version: your runtime is just the usable fuel in the tank divided by how hard your house is leaning on the generator. On a 500-gallon tank, most Florida homes ride out the better part of a week. The catch is that both of those numbers are sneakier than they look.

Get your address-specific installed price →

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

Your gauge stopped at 80, and that's on purpose

First thing that trips everybody up: you paid for a 500-gallon tank, you got it filled, and the needle parks at 80 percent. Feels like you got shorted. You didn't. Propane expands when it warms up, so every tank leaves the top empty on purpose — room for the liquid to breathe on a hot afternoon. It's the rule the whole industry fills to.

So your 500-gallon tank was never going to hold 500. Topped off, it's carrying around 400 gallons you can actually pull. Leave a little at the very bottom that the regulator can't draw cleanly, and 400 is your working number. That's not the fuel company nickel-and-diming you. That's just where the math starts.

The formula you're actually doing in the driveway

Once you know what's really in the tank, runtime is one line of division: usable gallons divided by how much the generator sips in an hour. That second number is the one people guess wrong.

Here's why. A portable generator at a job site is flooring it the whole time — full throttle, drinking fuel. A whole-home unit doesn't work that way. It throttles up and down to match whatever your house is pulling at that second, and most of a storm your house isn't asking for everything at once. So the engine spends most of its time nursing the tank instead of gulping it.

Picture the difference between idling in a drive-thru line and merging onto I-75 with your foot in it. A standby generator spends most of an outage in the drive-thru line. Which is why a tank that pencils out to a couple of days on a spec chart usually stretches into most of a week once it's running your real house.

The one thing that decides it: what your house is asking for

One of the sharpest things a homeowner said online was this — you can't figure fuel use until you know your load. Is the AC running? Is the dryer going? He's right, and in Florida there's really one answer that matters. The air conditioning.

Your AC is the biggest draw in the house by a mile, and in August it wants to run and run. That's the dial that turns runtime up or down. Crank the whole place cold and the generator leans in harder and drinks more. Let it hold around 77, close off a couple of rooms nobody's in, wait on the dryer until the sun's out — and the same tank carries you noticeably longer.

So the real answer to 'how long will my tank last' isn't a number off a chart. It's a question about how you plan to live for those few days.

Which is why you start with your address, not a chart

That's the part no online calculator can do for you. Your runtime rides on things that are specific to your house: the size of the tank sitting in your yard, the size of the generator you actually need, and how much of your particular home you want kept alive when the grid goes down. Undersize the generator and it strains. Undersize the tank and you're chasing a propane truck in the middle of a storm, right behind everybody else on your street.

So skip the chart and start with your house. Put your address into the price tool and GENERasic comes back with one committed installed number — the right-sized generator and the setup for your actual home, priced for real, not a range you have to decode. You stop doing panic math by flashlight and start with a plan that already fits your yard.

Common questions

What does it actually cost to run per day?

It depends on fuel price and how hard you lean on it, but plan on the generator drinking a couple of gallons an hour running the essentials, more if you're cooling the whole house. Over a multi-day outage that adds up — homeowners routinely report a few hundred dollars of propane across a week of a real storm. Set that next to a week of hotel rooms and a fridge full of spoiled groceries, and most people decide it's the cheap option.

The tank only reads 80% right after a fill. Did they short me?

No. Propane needs room to expand when it heats up, so tanks are filled to about 80 percent by code. A full 500-gallon tank reading 80 on the gauge is holding right around 400 usable gallons — exactly what you paid for. A gauge that read 100 would actually be the dangerous one.

Can I shut it off at night to stretch the fuel?

Plenty of people do — run it through the day, shut it down overnight once the AC load drops and everyone's asleep. It stretches the tank and gives the engine a rest. Just keep the house comfortable enough and the fridge and freezer doors shut, and they'll coast through the night no problem.

Do I really have to check the oil every day it runs?

Yes, and it's worth the two minutes. These air-cooled engines burn a little oil under long continuous runs, and a low crankcase during a five-day outage is how you cook the one machine keeping your house alive. Check it every morning, top it off, keep going.

Propane or natural gas — which one lasts longer in an outage?

They're really two different questions. Natural gas comes off the utility line, so it doesn't 'run out' as long as the line holds pressure — the worry there is whether the gas stays on, not runtime. Propane sits in your own tank in the yard, which means you control the supply but you're watching a gauge. In much of Florida propane is the practical pick because there's no gas line to the house, and a properly sized tank carries you through a typical outage with room to spare.

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 →