How Long Will A 100 Lb Propane Tank Last At 30,000 BTU? (Calculated)

100 lb propane tank running a 30,000 BTU patio heater, grill? Using propane energy density, we can calculate how long will a 100 lb propane tank last at 30,000 BTU. Important: We need to include non-100% propane burning efficiency as well.

Here’s how we can calculate how many hours/minutes 100 lb tank will last in a 2-step calculation:

1. Calculate how many BTUs will burning 100 lb of propane generate.
2. How long will these BTUs last on a 30,000 BTU heater, grill, etc.

Let’s start with the 1st calculation:

How Many BTUs Will Burning 100 Lb Of Propane Generate?

From EIA data, we see the following:

• 1 gallon of propane generates 91,452 BTU of heat (presuming 100% efficiency).
• Density of propane is 4.11 lb per gallon (at 77°F).

From this, we can calculate how many gallons of propane are in 100 lb propane tank:

100 lb Propane Tank = 100 lb / 4.11 lb/gallon = 24.33 Gallons Of Propane

Alright, so 100 lb of propane is equal to 24.33 gallons of propane.

Now, if we were to burn it with 100% efficiency, we get 91,452 BTU of heat per gallon. Thus, the whole 100 lb propane tank will generate:

100 lb Propane BTUs = 24.33 Gallons × 91,452 BTU/Gallon = 2,225,027 BTUs

We see that burning the whole 100 lb propane tank (at presumed 100% efficiency) will generate more than 2 million BTUs. Time for the 2nd calculation:

How Long Will 100 Lb Of Propane Last At 30,000 BTU?

Now, a patio heater, propane heater, grill, etc., burns through 30,000 BTU per hour. We know we have 2,225,027 BTUs in the tank. In theory (perfect 100% propane burning efficiency), here is how long we can run a 30,000 BTU/hr appliance:

Run Time (Theoretical 100% Efficiency) = 2,225,027 BTU / 30,000 BTU/hr = 74 Hours 10 Minutes

The key to making a useful real-time calculation is to understand that propane doesn’t burn at 100% efficiency. In most modern appliances, the propane burning efficiency ranges from 80% to 95%.

In practice, we can take a 90% burning efficiency, and, accounting for that, calculate how long will a 100 lb propane tank last at 30,000 BTU/hr appliance in practice like this:

Run Time (Practical 90% Efficiency) = 2,225,027 BTU × 0.9 / 30,000 BTU/hr = 66 Hours 45 Minutes

We see that 100 lb propane tank will last for 66 hours and 45 minutes at 30,000 BTU/hr. Hope this helps.