Propane is the outage fuel that waits patiently. It never goes stale, it burns in the cold that kills batteries, and one tank can run a generator, a heater, and a stove off the same supply. But a tank is just a number of pounds until you do this math: how many hours each appliance gets out of it, and how many days the whole set lasts at the pace you would actually run them. This planner does both. It sits alongside the gasoline math in our Generator Fuel & Runtime Calculator — same question, different fuel. No sign-up, and nothing you type leaves your browser.
Run your tank
A tank’s size is the propane it holds, not the steel’s full volume: tanks are filled to about 80 percent, so a “20 lb” tank really does carry about 20 pounds — roughly 4.6 gallons — of propane. The math here uses the size stamped on the collar.
Your appliances
| Appliance | Burn (BTU per hour) | Hours a day |
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A Worked Example
Take the defaults above: a 100 lb cylinder — about 2.16 million BTU of stored energy — running a dual-fuel generator six hours a day to keep the fridge and freezer cold and the batteries charged, plus a space heater eight hours a day to take the chill off one room. Together they draw 384,000 BTU a day, and the tank covers about five and a half days. Run alone, the generator would go 54 hours straight and the heater 120. Now swap the big cylinder for the 20 lb bottle off the grill and the same plan lasts about a day. That gap is the whole lesson of outage propane: the appliances are not the plan, the tank is. A row of grill bottles, refilled by rotation through the summer’s cooking, is a real strategy — one bottle by itself is a gesture.
How to Use This Planner
- Start with the tank you can actually get. If a 100 lb cylinder is not in the budget or the truck, run the plan on the bottles you own — two 20 lb tanks, rotated through the grill, is the most common real setup.
- Set burn rates from the appliance label. The presets are honest middles. Heaters run 9,000 to 30,000 BTU an hour depending on size; a generator at half load is near 40,000. Your label is the final word.
- Be honest about hours. A generator in an outage is a shifts machine — a few hours to chill the fridge and charge everything, then off. Planning it at 24 hours a day triples the fuel for comfort you will not use.
- Read the days line, then double the small loads. Lights, chargers, and the stove are rounding errors next to heat and generation. The heater’s hours are where plans live or die.
Propane Next to Gasoline
The trade is simple. Gasoline carries more energy per gallon and is sold on every corner, but it ages: untreated fuel is trustworthy for a few months, and even stabilized with something like STA-BIL it is on about a one-year clock, which means rotation forever. Propane carries about a quarter less energy per gallon and asks more of your storage setup, but the fuel in a sealed tank is as good in year ten as the day it was filled. That is why dual-fuel generators — the Champion 4250 is the one from our comparison — keep winning readers over: gasoline for the ordinary week, propane for the long one, and no carburetor ever gummed by its own storage. Our Preserve the Power hub holds the full picture.
Questions People Ask
How long does a 20 lb propane tank run a generator?
At the preset here — about 40,000 BTU an hour at half load — a 20 lb tank’s 432,000 BTU lasts roughly 11 hours of generation. Enough to matter across two or three days of shifts; nowhere near enough to run one around the clock. The generator’s size and load move this a lot, so set your own burn rate above.
Does propane really never go bad?
The fuel itself, yes — propane does not degrade in a sealed tank the way gasoline does. The tank is the clock instead: cylinders need recertification after 12 years, valves and hoses age, and a rusty tank is a hazard regardless of the fuel inside. Store tanks upright, outdoors or in a ventilated spot, never in a living space or a sealed basement.
Why does the tank feel emptier than the gauge math says, in deep cold?
Propane boils off inside the tank to feed the burner, and in hard cold that boil-off slows down — a nearly empty tank on a below-zero night may not push gas fast enough for a big load even with fuel left. It is one reason the big-cylinder plan beats the small-bottle plan in a winter outage.
Can I run my house furnace or water heater off a portable tank?
Those are plumbed appliances with their own regulators and line sizes — connecting a portable tank to house piping is a licensed-gas-fitter job, not a weekend project, and in many places not a legal one for a homeowner. This planner is for the portable side of the plan: generators, heaters, stoves, and grills with their own regulators.
Is storing several tanks safe?
Kept upright, outdoors or in a detached ventilated structure, away from ignition sources and out of living space, stored propane is one of the calmer fuels to keep. The rules that matter are boring: never indoors, never near a furnace or water heater, valves closed, caps on, and tanks off the ground if the spot floods.
The generators behind these numbers
All three are from our portable generator comparison and the classes this planner is built around:
Champion 4250 Dual Fuel Inverter
The dual-fuel pick: gasoline for the ordinary week, propane for the long one — the machine this page exists for.
WEN 56203i
The budget pick: the 2,000-watt class at the lowest buy-in — a second, smaller machine for the light-load hours is a real fuel strategy.
Honda EU2200i
The small-inverter benchmark: the quietest name in the class and easy on fuel at light loads.
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