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The power goes out on a still night, and the generator hums on the porch while the house waits for the grid. How long does a propane generator run? It runs as long as the propane in the tank and the load on the generator allow, and no listing here states the hours, so the answer is the tank size and the load, not a clock. This guide shows the tank sizes the listings state, what sets the burn, and the tank that must never feed a generator.
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How long does a propane generator run?
A propane generator runs until the tank is empty, and the tank size and the load set how soon that happens. The listings state tanks from 1 lb up to 100 lb, with the 100 lb tank stating a 23-gallon capacity and the 40 lb tank stating a 9.4-gallon capacity. A larger tank holds more propane and runs longer at the same load, and a heavier load burns propane faster. The listings state no run time in hours, so this guide gives no hours, only the figures the listings state.
Step 1: What sets the run time
What sets the run time is the propane in the tank and the load on the generator. A larger tank holds more propane. A heavier load draws more power and burns propane faster, so the same tank runs a shorter time under a heavy load than under a light one. The tank size is the figure the listings state, and the load is the figure the owner controls, by choosing what to plug in. See the dual fuel vs gas generators for the fuel choice.
Step 2: Tank sizes in the listings
The listings show Flame King steel tanks in 20, 30, 40 and 100 lb sizes, all refillable, all arriving empty and pre-purged, ready to fill. The 100 lb tank states a 23-gallon capacity and an item weight of 70.0 pounds. The 40 lb tank states a 9.4-gallon capacity. The 20 lb and 30 lb tanks state no gallon figure, only the pound size. The tanks state DOT and Transport Canada certification, with X-ray and hydrostatic checks, and an OPD valve to prevent overfilling.
| Tank size | Gallons stated | Gauge stated |
|---|---|---|
| 20 lb | Not stated | Built-in gauge on one listing |
| 30 lb | Not stated | Built-in gauge on one listing |
| 40 lb | 9.4 gallon | Not stated |
| 100 lb | 23 gallon | Not stated |
The gauge reads the gas level, so the tank never runs dry mid-run without warning.
Step 3: The load decides the burn
A generator sips propane at light load and drinks it at full load. The fridge, the lights and the phone chargers ask little of it, while a heater or a large motor asks much more. Plug in only what the run needs, and the tank lasts longer. The listings state no watts for these tanks, since a tank holds fuel and the generator sets the load, so the guide states no load figure here.
Step 4: Do not use a forklift tank
The 33.5 lb Flame King tank in the listings is a forklift tank with a liquid draw design, made to mount horizontally or vertically on a forklift. The listing states it is not compatible with BBQs or standard propane appliances, which require vapor draw, and that forklift tanks are designed for liquid draw, making them unsafe and incompatible. A generator takes vapor draw, like a grill or a heater, so use a vapor draw tank, not a forklift tank. Check the listing for the words liquid draw before connecting any tank.
Outdoors only
Fuel generators run outdoors only, far from doors and windows, because of carbon monoxide. The tanks state DOT and Transport Canada certification, and the OPD valve prevents overfilling, which the listings state is required by law in most states. Check the built-in gauge, where the listing states one, so the tank never runs dry mid-run.
Keep a spare tank ready
A spare tank turns a long outage from a race into a routine. Swap the empty tank for the full one, and the generator keeps running while the empty tank waits for a refill. The listings show the sizes side by side: a 20 lb tank for a short run, a 30 lb or 40 lb tank for a longer one, and a 100 lb tank for the longest runs. The gauge on the full tank shows the level before the swap, so the run starts on a full tank. A spare costs the tank and the fill, not another generator.
FAQ: power away from the grid
How long will a 20 lb propane tank run a generator?
The listings state no run time in hours, so the guide puts no hours on it. A 20 lb tank holds less propane than a 30 lb or 40 lb tank, so it runs a shorter time at the same load.
How long does a 100 lb propane tank last on a generator?
The 100 lb tank states a 23-gallon capacity, the largest here. It holds more propane than a 20, 30 or 40 lb tank, so it runs longer at the same load. The listings state no hours, so the exact run time depends on the generator and the load.
Can I use a forklift propane tank on a generator?
No. The 33.5 lb forklift tank states a liquid draw design for forklifts, and the listing states it is not compatible with BBQs or standard propane appliances, which require vapor draw.
How do I know how much propane is left?
The Flame King 30 lb tanks state a built-in gas meter gauge that provides gas level readings. Check the gauge before the run, and keep a spare tank on hand.
What size propane tank do I need for a generator?
Match the tank to the run you need: the listings show 20, 30, 40 and 100 lb tanks. A larger tank holds more propane and runs longer at the same load.
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