Honestly? When my neighbor Dave asked me this last week while firing up his grill, I almost gave him that useless textbook answer. You know the one: "It depends." But watching his eyes glaze over made me realize most articles skip the gritty details actual users need. Having run through more propane tanks than I'd like to admit (including that disastrous camping trip where we ran out mid-pancake breakfast), here's the no-BS breakdown.
The Single Biggest Factor People Ignore
Most folks think tank size tells the whole story. Big mistake. Your 20lb BBQ tank might last me 15 hours but only lasts my brother 8 hours. Why? Burn rate is king. That fancy infrared grill your cousin brags about? It gulps propane faster than my old clunker. I learned this the hard way when my new "upgrade" burned through a tank in two gatherings.
Appliance Types and Their Gas Guzzling Habits
| Appliance | Avg. Burn Rate (BTU/hr) | Tank Size | Realistic Runtime |
|---|---|---|---|
| Standard Gas Grill | 30,000-60,000 | 20 lb | 10-18 hours |
| RV Furnace | 25,000-40,000 | 30 lb | 12-20 hours |
| Patio Heater | 40,000-50,000 | 20 lb | 8-10 hours |
| Generator (5kW) | 75,000-100,000 | 100 lb | 10-14 hours |
| Gas Fireplace | 25,000-35,000 | 40 lb | 30-40 hours |
See that generator row? That's why hurricane prep guides tell you to stock extra tanks. Ran mine during the last outage thinking, "how long will a tank of propane last?" — 12 hours later: darkness. Not making that mistake again.
Your Exact Calculation Cheat Sheet
Math alert! But stick with me—this formula saved me hundreds:
Example for 20lb tank on 40,000 BTU grill:
(20 × 21,600) ÷ 40,000 = 432,000 ÷ 40,000 = 10.8 hours
Why 21,600?
Propane produces about 91,500 BTU per gallon. Since a 20lb tank holds about 4.7 gallons: 4.7 × 91,500 ≈ 430,000 BTU total. Divide by 20 lbs gives us 21,500 BTU per pound (we round to 21,600 for safety margins). Some argue it's 21,000 – but I err conservative after underestimating during deer hunting season.
Tank Sizes Decoded: More Than Just Pounds
| Tank Label | Actual Capacity | Common Uses | BTU Capacity |
|---|---|---|---|
| 20 lb BBQ Tank | Holds 4.7 gal (80% rule) | Grills, patio heaters | 430,000 BTU |
| 30 lb RV Tank | 7 gal | Travel trailers, camper heaters | 650,000 BTU |
| 40 lb Vertical | 9 gal | Large grills, garage heaters | 840,000 BTU |
| 100 lb | 24 gal | Generators, workshop heat | 2,160,000 BTU |
| 500 gal (Home) | 400 gal | Whole-house heating | 36,600,000 BTU |
Critical note: That "20lb" tank doesn't hold 20lbs of propane! Safety rules limit fill to 80%. So 20lb tank → 16lbs propane → 4.7 gallons. Miss this and your "how long does a tank of propane last" math fails.
7 Sneaky Factors That Slash Your Runtime
- Temperature Lies: Below 40°F? Propane contracts, reducing output. My turkey fryer tank lasted 25% less in November cold.
- Regulator Issues: Faulty regs cause flow surges. Replaced mine last year – gained 2+ hours per tank.
- Wind Theft: That patio heater battling 15mph winds? Burns 30% faster. My solution: DIY aluminum windbreak.
- Altitude Effects: Higher elevation = thinner air = more gas needed for combustion. Denver grills chug propane.
- Appliance Age: Clogged burners on my decade-old grill upped consumption by 15%. Clean those ports!
- Tank Position: Liquid propane must vaporize. Laying tanks sideways? Instant performance drop. (Don't ask how I learned)
- Leaks: $0.50 leak detector spray found my tank's valve leak costing me $8/month. Essential buy.
Extend Your Tank: Pro Tips They Don't Tell You
- The Hot Water Trick: Pour warm water down your tank's side. Frost line shows propane level. No gauge needed.
- Preheat Smart: Close grill lid during warm-up. Cut 5 minutes off startup = saves 2,500+ BTU.
- Pressure Check Hack: Weigh your tank empty (tare weight stamped on collar). Subtract from current weight. 1lb propane ≈ 4 hours on medium grill.
- Wind Defense: Use lava rocks in gas fire pits. Reflects heat, reduces burn rate 10-15%. Works wonders on my patio.
Real User Questions (That Aren't Answered Elsewhere)
Why does my propane tank freeze up?
Vaporization absorbs heat. During heavy use, tanks get cold. Frost means it's working hard – not malfunctioning. Wrap in insulating blanket if consistent issue.
Can propane expire while stored?
Nope. But tanks recertify every 5-12 years (check collar date). Old valves may leak. My 1998 tank failed last year – rusty valve stem.
Does a full tank last proportionally longer?
Mostly yes, but vaporization slows in cold when tank is low. That last 20% might deliver less pressure.
How long does a tank of propane last for home heating?
Brutally variable. My 500-gal tank (NE Ohio winter):
- At 20°F: Lasts ~3 weeks (70,000 BTU furnace)
- At 40°F: Lasts 5+ weeks
Insulation matters more than furnace efficiency!
The "When to Swap" Test I Use
Forget guessing. My field-tested method:
- Note start date/time when hooking up new tank
- Track appliance runtime hours (not calendar days!)
- When flame weakens: Weigh tank. If below 10% weight, swap.
Example log for my grill:
- Tank 1: Installed May 1 → Empty May 15 (14hrs total use)
- Tank 2: Installed May 16 → Current weight 14lbs (predicted empty June 4)
Propane Safety: What YouTube Won't Tell You
- Never store tanks indoors (garage included). My buddy's shed explosion proved why.
- Transport upright, secured. Loose tanks become missiles.
- Smell mercaptan (rotten eggs)? Shut off valve immediately. Don't "check connections first" – evacuate.
Personal Takeaways After 10+ Years
Honestly? Worrying about "how long does a tank of propane last" misses the point. Focus on efficiency. Since I:
- Cleaned my grill burners monthly
- Installed wind blocks
- Switched to infrared burner
My annual propane cost dropped $140. That tank runtime obsession? Gone. Now I track cost per hour.
Final thought: Your mileage will vary. Track your usage religiously for 2 months. You'll get better answers than any chart gives.
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