How long will a 20 lb propane tank last on a gas fire pit?

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Figure roughly 8 to 10 hours on a moderate flame and about 5 hours wide open on a big burner — a full 20 lb grill tank holds about 4.6 gallons (around 420,000 BTU), and a gas fire pit pulls 50,000 to 90,000 BTU an hour on high. Ease off the flame and you'll stretch it well past that.

The rough math

A filled 20-pound cylinder carries about 4.6 gallons of propane, and each gallon delivers roughly 91,000 BTU — call it 420,000 BTU in the tank. A gas fire pit on full blast — anywhere from 50,000 to 90,000 BTU an hour; the Napoleon Uptown we carry runs 60,000 — drains it in roughly five to eight hours. Dial it back to a relaxed evening flame and one tank carries you through a couple of cool mountain nights. Nobody runs a fire pit flat-out the whole time, so real-world life usually lands in the eight-to-ten-hour neighborhood.

Cold weather shortens it

Here's the wrinkle we see every fall: a small cylinder frosts up and loses pressure when it's working hard in the cold. Propane has to vaporize inside the tank to feed the burner, and pulling a lot of fuel fast on a 40-degree evening can chill the tank until it can't keep up — the flame shrinks even with propane still sloshing inside. That's normal for a 20-pounder pushed hard, not a defect. Warmer nights and lower settings avoid it.

When a bigger supply makes sense

If you're refilling a grill tank every couple of evenings, it's often worth running a permanent gas line to your fire pit from a stationary tank or a natural-gas main instead — no swapping, no frosting, no running dry mid-s'more. That's licensed work, and it's our lane: we run and permit the outdoor-rated line and set the pit up for your fuel. Call (828) 545-0525 to talk it through.

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