Let’s say you have a 30,000 BTU propane heater, grill, patio heater, etc. They come with 20 lb propane tanks. The question we are going to address here today is this:
How many hours will a 20 lb propane tank last at 30,000 BTU output?
First of all, we need to calculate how much energy (in terms of BTU or British Thermal Units) will burning 20 lb of propane generate. They we will calculate for how long can this energy from burning 20 lb of propane sustain a 30,000 BTU/hr patio heater, grill, etc:
20 lb Of Propane BTU Production
According to EIA (US Energy Information Administration), 1 gallon of propane can produce 91,452 BTU of heat. If we check the propane weight per gallon here, we see that (at 77ยฐF) 1 gallon of propane weighs 4.11 lb.
Now, since we have 20 lb of propane and propane density is 4.11 lb/gallon, we can calculate how many gallons of propane are in 20 lb tank like this:
20 lb of Propane = 20 lb / 4.11 lb/gallon = 4.866 gallons
We see that 20 lb of propane contains 4.866 gallons of propane. Since we know that 1 gallon of propane can produce 91,452 BTU of heat, we can calculate how much heat can 20 lb or 4.866 gallons of propane produce like this:
Energy Capacity (20 lb of propane) = 4.866 gallons ร 91,452 BTU/gallon = 445,005 BTU
Alright, now we know that 20 lb propane cylinder contains 445,005 BTU of energy if we burn it at 100% efficiency. Let’s calculate how long this will run a 30,000 BTU/hr heater:
How Long Will 30,000 BTU Heater Run On 20 lb Propane Tank?
If propane would burn at 100% efficiency, we can quickly calculate how long 20 lb of propane would fuel a 30,000 BTU/hr heater like this:
Running Time = 445,005 BTU / 30,000 BTU/hr = 14 Hours 50 Minutes
At 100% propane burning efficiency, you run a 30,000 BTU/hr heater for almost 15 hours.
However, propane heaters and patio heaters don’t run at 100% efficiency. Rather, modern propane heaters have between 80% and 95% efficiency. Thus, in our calculations, we need to take a practical 90% efficiency. We can now calculate how long will a 20 lb propane power a 30,000 BTU/hr heater in practice:
Running Time (In Real World) = 0.9 ร 445,005 BTU / 30,000 BTU/hr = 13 Hours 21 Minutes
We see that practically, a 20 lb propane tank will run a 30,000 BTU/hr heater for 13 hours and 21 minutes. That’s enough for a whole afternoon of grilling or whole night of running a patio heater.
We hope you now have a good understanding of how to make these calculations. If you need a bit of our input, you are always welcome to use the comments below to explain what you want to calculate, and we can help you out.