Propane is a popular fuel source for heating, cooking, and powering various appliances. It comes in portable tanks that range in size from small 1 lb cylinders to large 100 lb tanks. A common size for home and recreational use is the standard 20 lb propane tank.
Quick Answer
A full 20 lb propane tank contains about 18-20 lbs of actual propane liquid. The energy content of propane is about 91,500 BTU per gallon. Since there are about 4.7 gallons in a 20 lb tank, the total BTU is:
4.7 gallons x 91,500 BTU/gallon = 430,500 BTU
So a full 20 lb propane tank contains approximately 430,500 BTU of heat energy.
Detailed Answer
Let’s break this down step-by-step:
1. Weight of propane in a 20 lb tank
Although referred to as 20 lb tanks, the actual weight of propane contained is slightly less:
- Empty tank weight: 17 lbs
- Full tank weight: 37 lbs
- So propane weight is 37 – 17 = 20 lbs
However, because propane is a liquid gas under pressure, not all 20 lbs is actual propane fuel. Some weight is attributed to the tank itself and residual gas vapors. Once the pressure is released as propane is used, there is often 18-20 lbs of actual propane liquid remaining in a “empty” 20 lb tank.
2. BTU per gallon of propane
The energy content of propane is about 91,500 BTU per gallon of liquid propane fuel. This can vary slightly by the purity and composition of the propane.
3. Gallons of propane in a 20 lb tank
With about 18-20 lbs of actual propane fuel in a 20 lb tank, we can calculate the gallons using the density of propane:
- Density of propane = 4.24 lbs/gallon
- 20 lbs / 4.24 lbs/gal = 4.72 gallons
Rounding down slightly for variations in tanks, let’s assume 4.7 gallons of propane in a full 20 lb tank.
4. Calculate total BTU
Given:
- Gallons of propane = 4.7
- BTU per gallon = 91,500
Total BTU = Gallons x BTU/Gallon
= 4.7 x 91,500
= 430,500 BTU
Key Takeaways
- A standard 20 lb propane tank contains about 18-20 lbs of actual propane fuel.
- The energy density of propane is around 91,500 BTU per gallon.
- Given the density of 4.24 lbs/gallon, a 20 lb tank holds about 4.7 gallons of propane.
- Multiplying the gallons by the BTU per gallon, we get approximately 430,500 BTU in a full 20 lb propane tank.
Usage Table
Here is a table showing approximate BTU usage times for common propane appliances running on a full 20 lb tank:
| Appliance | BTU/Hr | Hours of Use |
|---|---|---|
| Gas grill | 25,000 | 17 |
| Outdoor patio heater | 40,000 | 10 |
| RV water heater | 8,800 | 48 |
| RV furnace | 20,000 | 21 |
This table illustrates how a 20 lb propane tank can supply gas for extended use of appliances when camping or during a power outage. For example, it could run a patio heater for up to 10 hours or RV water heater for 2 days continuously.
Refilling 20 lb Propane Tanks
When your 20 lb propane tank runs out, you will need to get it refilled. Here are some tips for refilling propane tanks:
- Many retailers like hardware stores, gas stations, and camping/RV suppliers offer propane refilling services.
- Cost is typically $15-$25 to refill a 20 lb tank, or about $1.50-$2.00 per gallon of capacity.
- Make sure to specify you need a 20 lb tank filled, as other sizes are available.
- Only certified professionals should refill propane tanks, as improper refilling can be extremely dangerous.
- Inspect tank valves, connectors, and hoses regularly for leaks and damage.
- Consider getting a spare/backup tank so one can be refilled while the other is in use.
Propane Tank Sizes
20 lb cylinders are a very common size, but propane tanks come in many other capacities as well. Here are some of the most popular propane tank sizes:
- 1 lb – Small disposable cylinders for portable stoves or torches.
- 5 lb – Lightweight tanks for tailgating, camping stoves, snow melting.
- 10 lb – Portable tanks for moderate usage in RVs or with outdoor heaters/grills.
- 20 lb – Versatile standard size for home, workshop, RV uses.
- 30 lb – Similar capacity to 20 lb but larger and heavier duty.
- 40 lb – Large tank for extended high demand usage.
- 100 lb – Extra large tank for commercial and residential applications.
Make sure to select the appropriate size based on your expected propane usage and appliance requirements. The 20 lb tank offers a good balance of portability and runtime for many applications.
Propane Safety
Propane is an excellent fuel source but also requires safety precautions. Here are some key propane safety tips when using 20 lb tanks:
- Always store upright and secure tanks firmly so they don’t tip over.
- Keep outdoors or in well ventilated areas away from heat/flame sources.
- Close tank valves when not in use to prevent leaks.
- Check hoses for wear/damage and ensure fittings are tight.
- Never transport tanks inside an enclosed vehicle.
- Place protective collars around tank valves during storage/transport.
- Keep away from enclosed spaces, basements, pits, below grade.
- Do not expose tanks to high heat (above 120°F) which could cause pressure buildup.
- Have certified professionals handle tank refills/maintenance.
Following basic safety precautions will help ensure safe, reliable operation of propane appliances fueled by 20 lb tanks.
Propane vs Natural Gas
Propane and natural gas are both common fuel sources for heating and cooking appliances. They have some key differences:
| Propane | Natural Gas |
|---|---|
|
|
Propane offers more portability and independence, while natural gas provides greater convenience in urban areas. Both can effectively power many appliances. Choose based on your needs and what is available in your region.
Conclusion
A standard 20 lb propane tank contains about 18-20 lbs of actual propane fuel, which equals around 4.7 gallons. With propane having an energy density of 91,500 BTU/gallon, this means a full 20 lb propane tank holds approximately 430,500 BTU of heat energy.
This amount of propane can supply gas for 10-48 hours of usage depending on the appliance. 20 lb cylinders are a popular size due to their versatility for many home, recreational, and commercial applications. With proper safety precautions, 20 lb propane tanks offer an efficient and convenient fuel source for a variety of propane-powered equipment.
