How Long Does a 20 lb Propane Tank Last on a Fire Table? The Real Math
Every fire table buyer asks this eventually, and most answers online are vague. The math is actually simple, so here it is with real numbers.
The short answer
A standard 20 lb propane tank runs a typical gas fire table for about 7 to 11 hours on high, and roughly double that at half flame. Where you land in that range depends on one number: your burner's BTU rating.
The math (so you can check it yourself)
Propane contains about 21,500 BTU per pound. A full 20 lb tank therefore holds:
20 lb × 21,500 BTU/lb ≈ 430,000 BTU
Your fire table's burner is rated in BTU per hour — that's its maximum draw at full flame. Divide tank capacity by burner rating and you have runtime on high:
| Burner rating | Runtime on high | Runtime at ~50% flame |
|---|---|---|
| 40,000 BTU | ~10.7 hours | ~21 hours |
| 45,000 BTU | ~9.5 hours | ~19 hours |
| 50,000 BTU | ~8.6 hours | ~17 hours |
| 60,000 BTU | ~7.2 hours | ~14 hours |
Most gas fire tables sit in the 40,000–60,000 BTU range. Our Carrara marble porcelain fire table, for example, runs a 60,000 BTU stainless burner — at a comfortable evening flame setting you'll get several nights of use from one tank, not one.
What that costs per hour
A 20 lb refill typically costs $20–$25 at a propane dealer or hardware store (tank exchanges run $25–$30 and often give you only 15 lb of fill — refill, don't exchange, when you can). At $22 per refill:
- Full flame at 60,000 BTU: roughly $3.00/hour
- Moderate flame: roughly $1.50/hour
Propane vs. natural gas cost
If your fire table runs on a natural gas line instead, the same 60,000 BTU/hour on high consumes about 0.6 therms. At typical residential rates ($1–$2 per therm), that's $0.60–$1.20 per hour — roughly a third of propane's cost. The tradeoff is the one-time cost of running the line (commonly a few hundred dollars depending on distance and local rates) and losing the ability to reposition the table. We covered the full decision in our propane vs. natural gas guide.
Five things that change your real-world runtime
- Flame setting is everything. The BTU rating is maximum draw. Most evenings you'll run 40–60% flame, which extends runtime proportionally.
- Wind. A windy patio makes people crank the flame higher to keep the same visual presence. Wind guards help.
- Cold weather reduces tank pressure. Below roughly 20°F, a nearly-empty propane tank can struggle to vaporize fuel fast enough for a large burner. Keep tanks fuller in winter.
- Partial fills. Exchange tanks are frequently filled to 15 lb, not 20 — that's 25% less runtime before you've lit the burner.
- Burner efficiency doesn't vary much — a CSA-certified stainless burner at 50,000 BTU burns the same fuel as any other 50,000 BTU burner. Buy for build quality and warranty, not efficiency claims.
How to tell how much propane is left
No gauge? Pour hot tap water down the side of the tank, then run your hand down it. The metal turns cool at the liquid propane line. A 20 lb tank weighs about 17 lb empty (check the stamped tare weight, "TW") and about 37 lb full — a luggage scale gives you an exact reading in seconds.
FAQ
Should I keep a spare tank?
Yes. Nothing ends a dinner party faster than a dead tank at 8pm. Most fire table bases with tank enclosures fit one tank, so store the spare elsewhere — outdoors, upright, never in the house or garage.
Can I use a larger tank?
Usually, yes — a 30 or 40 lb tank connects the same way but won't fit inside most fire table bases. Many owners run a longer hose to a larger tank hidden beside the seating area for 50–100% more runtime.
Does a higher BTU table waste gas?
No — higher-rated burners give you more headroom, not mandatory consumption. A 60,000 BTU table dialed to half flame burns like a 30,000 BTU table at full.
Tyler runs Backyard Pyre, where every fire table and fire bowl we sell — from $849 concrete bowls to marble porcelain dining tables — ships in both propane and natural gas versions.