This is a common question for people using propane tanks to fuel appliances like grills, portable heaters, generators and more. The short answer is that a standard 20 lb propane tank containing 4.7 gallons of propane will last approximately 10 hours at 50,000 BTU.
But to fully understand this, we need to look at the details of BTU ratings, tank sizes, and propane burn rates. We’ll also provide tips on how to make your propane tank last longer.
What is a BTU?
BTU stands for British Thermal Unit, and it is a standard measurement of heat energy. Specifically:
- 1 BTU = the amount of heat required to raise 1 pound of water by 1 degree Fahrenheit
- 1 BTU ≈ 0.0002931 kilowatt-hours (kWh)
Appliances like grills and heaters have a BTU rating that indicates their heat output capacity. The higher the BTU rating, the more heat the appliance can produce.
Standard 20 lb Propane Tank Specs
A standard 20 lb propane tank used for home grilling and portable appliances has these specs:
- Empty Weight: 18-20 lbs
- Filled Weight: 38-43 lbs
- Dimensions: 18″ (height) x 12.5″ (diameter)
- Capacity: 4.7 gallons of propane when full
The term “20 lb” refers to the empty weight of the cylinder. When completely filled, the tank holds about 20 lbs of propane liquid.
Propane Burn Rates
An appliance’s BTU rating can be used to calculate its propane consumption, also known as the burn rate. Here are some example burn rates:
- 10,000 BTU = 0.96 lb/hour
- 20,000 BTU = 1.92 lbs/hour
- 30,000 BTU = 2.88 lbs/hour
- 40,000 BTU = 3.84 lbs/hour
- 50,000 BTU = 4.8 lbs/hour
So an appliance rated at 50,000 BTU will consume propane at a rate of 4.8 lbs per hour.
How Long Will a 20 lb Propane Tank Last at 50,000 BTU?
Now we can estimate how long a full 20 lb propane tank will last while operating an appliance at 50,000 BTU:
- Capacity of a full 20 lb propane tank = 20 lbs of propane
- Propane consumption at 50,000 BTU = 4.8 lbs/hour
- 20 lbs propane ÷ 4.8 lbs/hour = 4.2 hours
So a 20 lb propane tank will last around 4 hours if an appliance is continuously drawing 50,000 BTU. Because appliances aren’t always running at full capacity though, we can estimate the tank will last around 8-10 hours for typical real-world use.
Factors That Affect Propane Runtime
There are several factors that can impact how long your propane tank will last:
Tank Fill Level
If your tank is less than full, it will have less than 20 lbs of propane and won’t last as long. Only a fully filled tank contains the full 20 lbs of propane.
Appliance BTU Input
Higher BTU appliances use more propane. A 50,000 BTU appliance will consume propane twice as fast as a 25,000 BTU unit.
Appliance Burner Output
Appliances often have adjustable burner/heating levels. Using a lower output level will consume less propane and extend tank life.
Ambient Temperature
In cold weather, appliances have to work harder (use more propane) to generate heat.
Wind Conditions
Windy conditions can disrupt appliance burners and cause them to consume more propane.
Tank Condition
Tanks can gradually corrode or develop small leaks over time, resulting in lower capacity and shorter runtime.
Tips for Conserving Propane
Here are some tips to help your propane tank last longer:
- Start with a full 20 lb tank
- Set appliance to lowest necessary flame/heat
- Keep outdoor appliances sheltered from wind
- Use an appliance cover to retain heat
- Preheat gradually – avoid high heat food searing
- Turn off appliance when not in use
- Inspect tank valves/hoses for leaks
- Consider getting a tank gauge to monitor fuel level
Using Larger Propane Tanks
If you need more extended propane runtime, consider upgrading to a larger tank. Here’s how long different propane tanks will last at 50,000 BTU:
| Tank Size | Propane Capacity | Estimated Runtime at 50,000 BTU |
|---|---|---|
| 20 lbs | 4.7 gallons | 8-10 hours |
| 30 lbs | 7.5 gallons | 13-16 hours |
| 40 lbs | 9.9 gallons | 17-22 hours |
| 100 lbs | 24 gallons | 42-50 hours |
As you can see, upgrading to a larger 100 lb propane tank can provide over 5 days of continuous runtime for a 50,000 BTU appliance. But the larger tanks are more cumbersome to transport and refill.
Using Multiple 20 lb Tanks
Another option is to use multiple standard 20 lb propane tanks and swap them out as needed. This provides more runtime than a single tank, with more convenience than a large 100 lb cylinder.
Using two 20 lb tanks effectively doubles your runtime over a single tank. Some propane appliances allow you to connect two tanks at once for even longer continuous operation.
Refilling Propane Tanks
When your propane tank runs out, you will need to get it refilled. Many retailers like hardware stores, gas stations, and camping supply outlets provide propane refilling services.
The current average price to refill a 20 lb propane tank is around $15-$20. Larger tanks cost more to refill. You can save money by refilling when propane prices are lowest in the summer months.
Safety Tips for Propane Tanks
When using and handling propane tanks, be sure to follow these safety guidelines:
- Never overfill tanks beyond recommended capacity
- Store and transport tanks securely in an upright position
- Keep tanks outdoors and away from heat/flame sources
- Check tank valves, connectors, and hoses for leaks and damage
- Don’t modify or try to repair valves yourself
- Place tanks so the relief valve aims away from people/structures
Conclusion
To estimate propane runtime, you need to know the tank size, propane capacity, and the appliance BTU rating. A standard 20 lb propane tank contains 20 lbs of propane and will last approximately 8-10 hours on an appliance burning 50,000 BTU.
Larger tanks provide more runtime, but are less portable. Using multiple 20 lb tanks is often a good compromise for extended propane capacity. Be sure to follow safety guidelines when using and storing propane tanks.