Propane Heater Run Time Calculator

Heat in a pound of propane

The U.S. Energy Information Administration lists propane at 91,452 BTU per gallon, and a gallon of liquid propane weighs 4.24 lb. That works out to about 91,452 ÷ 4.24 ≈ 21,570 BTU per lb.

A heater's BTU number is how much heat it burns in an hour. So hours of burning is pounds of propane × 21,570 ÷ heater BTU per hour. A Buddy on high (9,000 BTU) burns through a 1 lb cylinder in about 2.4 hours.

Hours of heat and your trip

If you only keep the heater lit part of the time, the same propane lasts longer: hours of heat = hours of burning ÷ share of time it is on. Your trip needs hours a day × days.

Propane for the trip is trip hours × share on × BTU per hour ÷ 21,570, rounded up to whole cylinders or tanks.

How close this is to Mr. Heater's numbers

• Little Buddy, 3,800 BTU on 1 lb: Mr. Heater says 5.6 h, we get 5.7 h.
• Hunting Buddy on 1 lb: 3.5 h and 1.8 h listed, we get 3.6 h and 1.8 h.
• Buddy FLEX on high, 1 lb: 2 h listed, we get 2.0 h.
• Big Buddy on two 1 lb: 11 h and 4.8 h listed on low and medium, we get 10.8 h and 4.8 h.
• On a 20 lb tank: Buddy 48 to 110 h listed, we get 48 to 108 h. Big Buddy 24 to 108 h listed, we get 24 to 108 h.
• Higher on the box: Buddy on 1 lb is listed at 6 h low and 3 h high, we get 5.4 h and 2.4 h. Big Buddy on high (two 1 lb) is listed at 2.8 h, we get 2.4 h.

So 10 of the 13 published figures land within 3% of our math. The other three are 11 to 25% higher than the heat in the propane allows at that BTU rating, so we use the lower number. Plan on it and you won't come up short.

Exchange tanks and cold weather

A 20 lb exchange tank, like Blue Rhino, is filled with 15 lb of propane, not 20. A tank you get refilled holds 20 lb. That is a quarter less heat from the swap tank.

The Buddy and Big Buddy manuals warn that run times can be much shorter when running nonstop below 20 °F, because of how propane behaves in the cold, and recommend a 20 lb tank then. They don't give a number, so the calculator doesn't cut the hours. It warns you instead. The Buddy is rated down to 0 °F.

What it leaves out

• Cylinders that aren't full, and propane left in a tank when the pressure gets too low to run the heater.
• How warm the space gets. That depends on the size of the blind or shanty, wind, insulation and the vents you open.
• Heaters at high altitude. Buddy heaters may shut off above 7,000 ft.

Sources

• U.S. EIA: British thermal units (propane, 91,452 BTU per gallon)
• AmeriGas: BTU per gallon of propane (a gallon weighs 4.24 lb)
• Mr. Heater Portable Buddy (MH9BX) manual: 4,000 / 9,000 BTU, 3 to 6 h on 1 lb, 48 to 110 h on 20 lb, 9 sq in vents, never operate while sleeping, below 20 °F note, hoses and filter
• Mr. Heater Big Buddy manual: 24 to 108 h on 20 lb, 18 sq in vents, never operate while sleeping
• Mr. Heater Big Buddy (MH18B) spec sheet: 4,000 / 9,000 / 18,000 BTU, 11 / 4.8 / 2.8 h on two 1 lb
• Mr. Heater Little Buddy (MH4B): 3,800 BTU, 5.6 h on 1 lb, 1 lb cylinders only
• Mr. Heater Hunting Buddy (MH12HB): 6,000 / 12,000 BTU, 3.5 h low and 1.8 h high on 1 lb (manufacturer answer)
• Mr. Heater Buddy FLEX (MH11BFLEX): 11,000 BTU max, 2 h on 1 lb at max
• Mr. Heater hoses and fuel filter FAQ
• Ace Hardware: Blue Rhino 20 lb exchange tanks hold 15 lb
• CPSC: portable heaters and camping equipment
• CDC: you can prevent carbon monoxide exposure