How Long Does Propane Last in a Mr. Heater Big Buddy? (Run Times Chart)

The Short Answer: How Long Propane Lasts

One of the most common questions I get is: how long will a Mr. Heater Big Buddy run on a 20 lb propane tank? It is a great question, and the answer depends on which heat setting you use. In this guide, I will break down the exact run times for the Mr. Heater Big Buddy (model MH18B) on low, medium, and high settings, using both 1 lb canisters and 20 lb tanks.

Mr. Heater Big Buddy BTU Settings and Burn Rates

The Mr. Heater Big Buddy (MH18B) has three heat settings:

• Low: 4,000 BTU/hr
• Medium: 9,000 BTU/hr
• High: 18,000 BTU/hr

Propane contains approximately 21,548 BTU per pound. A standard 20 lb propane tank holds about 16-17 lbs of usable propane when full (tanks are filled to 80% capacity for safety). That gives you roughly 344,000-365,000 BTU of usable energy per tank.

How Long Will a 20 lb Tank Last on Each Setting?

Here is the breakdown based on the BTU burn rate and the usable propane in a 20 lb tank:

• Low (4,000 BTU): Up to 108 hours (about 4.5 days of continuous use)
• Medium (9,000 BTU): Up to 48 hours (about 2 days of continuous use)
• High (18,000 BTU): Up to 24 hours (about 1 day of continuous use)

Keep in mind these are ideal calculations. Real-world run time varies based on ambient temperature, wind, altitude, and whether your tank is completely full. In my testing, I found the actual run times to be slightly shorter than the theoretical maximums, especially on high.

How Long Will 1 lb Canisters Last?

A 1 lb propane cylinder holds roughly 21,548 BTU of energy. Here is how long each setting will run on a single 1 lb canister:

• Low (4,000 BTU): Up to 5.4 hours
• Medium (9,000 BTU): Up to 2.4 hours
• High (18,000 BTU): Up to 1.2 hours

The Big Buddy can run on two 1 lb canisters simultaneously, which doubles those run times. With two canisters on low, you get about 10-12 hours of heat. On high, you get about 2.5-3 hours.

Real-World Factors That Affect Run Time

In my video testing, I found several factors that affect how long your propane actually lasts:

• Temperature: Cold propane tanks have lower vapor pressure, which can reduce flow rate and effective BTU output.
• Altitude: At higher elevations, propane burns less efficiently. The Big Buddy is rated for use up to 7,000 feet above sea level.
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• Wind and drafts: Even though the heater is indoor-safe, drafts can carry heat away and cause the unit to cycle more.
• Heater condition: A dirty or partially clogged burner will not burn efficiently, reducing both heat output and fuel economy.

Should You Use 1 lb Canisters or a 20 lb Tank?

For short-term use like a weekend camping trip or a few hours of emergency heat, 1 lb canisters are convenient and simple. For anything longer, a 20 lb tank is the way to go. The cost per BTU is dramatically lower with a 20 lb tank, and you avoid the waste of disposable cylinders.

If you want to use a 20 lb tank with your Big Buddy, you will need a hose and filter. I cover exactly how to set that up in my article on connecting a Mr. Heater to a 20 lb tank, and I also address whether a fuel filter is necessary (spoiler: it is).

Cost Comparison: 1 lb vs 20 lb Propane

Here is a quick cost breakdown to show why upsizing to a 20 lb tank saves money:

• 1 lb canister: About $5-8 each at retail. That is roughly $0.23-0.37 per 1,000 BTU.
• 20 lb tank exchange: About $20-25. That is roughly $0.06-0.07 per 1,000 BTU.
• 20 lb tank refill: About $15-18. That is roughly $0.04-0.05 per 1,000 BTU.

Refilling a 20 lb tank is roughly 5-8 times cheaper per BTU than buying disposable 1 lb canisters. If you use your heater regularly, the savings add up fast.

Tips to Maximize Propane Efficiency

• Use the lowest heat setting that keeps your space comfortable. Dropping from high to medium more than doubles your run time.
• Insulate and seal the room you are heating. The Big Buddy is rated for up to 400 sq ft, but a well-insulated smaller space will stay warm longer on less fuel.
• Keep the heater clean. Dust and debris in the burner tiles reduce efficiency.
• Store propane tanks upright and outdoors, never inside the living space.
• Consider a refillable 1 lb cylinder system if you want the convenience of small canisters without the waste.

Safety Reminders

The Mr. Heater Big Buddy is indoor-safe thanks to its built-in oxygen depletion sensor (ODS) and tip-over switch. But that does not mean you can skip basic safety:

• Always provide adequate ventilation. The manual recommends at least 6 square inches of fresh air opening.
• Never use the heater in a sleeping area without a working ODS.
• Keep propane tanks outside. Only the heater goes inside.
• Check hoses for cracks before each use if you are running a 20 lb tank.
• Install a battery-powered carbon monoxide detector in any room where you use a propane heater.

Get the Mr. Heater Big Buddy: Buy on Amazon | Buy at Lowe’s. For more on Mr. Heater safety, check my article on the Little Buddy heater and my safety warning about what NOT to do with your Mr. Heater.

Conclusion

The Mr. Heater Big Buddy is one of the most reliable indoor propane heaters you can own. On a 20 lb tank, you can expect anywhere from 24 hours on high to over 100 hours on low. For most people, running on low or medium in a well-insulated room is the sweet spot for both comfort and fuel economy.

If you found this helpful, check out my YouTube channel for more homesteading and off-grid content, and visit shopeth.link for current links and discount codes on propane heaters and accessories.