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The cleanest way to run a generator from two propane tanks is an automatic changeover regulator, the same kind used on RVs and many homes. Two cylinders connect to it. It draws from one until it’s empty, then switches to the other, so you can swap the empty one without shutting down. A listed tee or manifold that ties two cylinders into one line also works, as long as every part is rated for propane and the pressures match your generator.
Why bother with a second tank
- Run time. A 20 pound cylinder holds about 4.7 gallons. A mid-size dual-fuel portable can empty it in several hours under load.
- Cold weather. A cylinder can only vaporize propane so fast, and that rate drops as it gets colder. Two cylinders feeding together supply more vapor.
- No-stop swaps during long outages.
Choose a connection method
| Method | How it works | Notes |
|---|---|---|
| Automatic changeover regulator | Draws from the “service” cylinder, then switches to “reserve” | Must match the generator’s required inlet setup. Many portables expect cylinder pressure into their own regulator. |
| Tee or manifold with pigtails | Both cylinders feed one line at the same time | Use listed parts. Open both valves for maximum vapor supply. |
| Larger cylinders (100 lb) | One bigger tank instead of two small ones | About 23.6 gallons. Heavy, and must be delivered or filled in place. |
Check the regulator pressure before anything else
This is the step people get wrong. Most portable dual-fuel generators come with a hose and regulator meant to connect directly to a cylinder. Some expect high (cylinder) pressure to an onboard regulator, and others low pressure. Standby generators specify an inlet pressure. Generac’s Guardian sheets, for example, call for 10 to 12 inches of water column on LP. Use the setup your manual specifies. Adding a second regulator in the wrong place can starve the engine.
Connecting the two cylinders
- Place cylinders upright, on a stable surface, outdoors, away from the generator’s exhaust and hot surfaces.
- Connect the pigtails or manifold and tighten the fittings. Many propane fittings are reverse-threaded.
- Open the valves slowly.
- Leak-test every joint with soapy water. Bubbles mean a leak. Never use a flame.
- Start the generator as the manual describes for propane.
In cold weather
- Propane vaporizes more slowly as it gets colder. A 20 pound cylinder that keeps up on a mild day may not in freezing weather.
- Feeding from two cylinders at once, or using a 100 pound cylinder, supplies more vapor.
- Never heat a cylinder with a flame or heater to improve flow.
- Frost on the outside of a cylinder shows where the liquid level is, and that it’s working hard.
How long two cylinders last
Burn rates vary by generator and load. A portable in the 7,000 watt class on propane might use roughly 0.7 to 1 gallon an hour at half load, according to typical manufacturer charts. Two 20 pound cylinders (about 9.4 gallons) would last roughly 9 to 13 hours. Check your model’s figures and use the fuel run-time calculator.
Code rules for cylinders and hoses
- Propane storage and use are governed by NFPA 58 and your local fire code. Spare cylinders belong outdoors, never in a garage or basement.
- Keep cylinders away from building openings and air intakes. See how far a propane tank should be from a generator.
- Close the cylinder valves when not in use.
The setups that cause trouble are usually improvised:
- Homemade manifolds from non-rated fittings.
- Laying cylinders on their sides, which can send liquid propane into the line.
- Using a hose too short to keep the cylinders away from the hot exhaust.
For permanent connections, such as large tanks or piping to a fixed generator, use a licensed propane installer.
More on running a generator from two tanks
Can I hook my generator to my house propane tank? Yes, with a properly installed connection. See connecting a generator to your home’s propane supply.
Can I use an RV’s onboard propane for a portable generator? Only with a properly installed quick-connect port and the correct pressure for your generator.
Can I mix a 20 pound and a 100 pound cylinder? Yes, with a changeover regulator or manifold. Each connects through its own pigtail.
More in the fuel hub.
