How Long Does A Propane Tank Last On A Patio Heater? (7.57-37.86h)

If you have a patio heater, it’s probably powered by propane. 20 lb propane tanks are the most common ones; some outdoor patio heaters can also have 30 lb tanks. We will calculate how long does a propane tank last on a patio heater.

To properly estimate how many hours will a 20 lb propane tank last, we need to consider these 2 factors:

1. Patio heater BTU capacity. Small patio heaters generate 10,000 BTU of heating output and large patio heaters generate 50,000 BTU of heating output. Obviously, the 50,000 BTU patio heater will drain the propane tank much faster than the 10,000 BTU heater (5-times faster, in this case). Depending on the BTU capacity, patio heaters can last anywhere from 7.57 hours to 37.86 hours on a 20 lb propane tank (more in the table further on).
2. Propane burning efficiency. Propane in a patio heater doesn’t burn at 100% efficiency. Most propane patio heaters burn propane at 80% to 95% efficiency. In our calculation, we will presume we’re dealing with an average 90% efficiency patio heater.

The latter factor means that if a certain outdoor propane heater lasts 10 hours theoretically, it will only last 9 hours in practice. That’s because 10% of propane’s energy content is wasted.

First, we will calculate how many BTUs does a 20 lb tank of propane holds. Then we will estimate how long will propane patio heaters with 10,000 to 50,000 BTU heating capacity last. You can find all the times (for all heating capacities) in the table further on.

How Much Useful Energy Does A 20 lb Propane Tank Contain?

According to the EIA, 1 gallon of propane has an energy content of 91,452 BTU. With outdoor patio heaters, we’re dealing with 20 lb propane tanks; that’s a 4.6-gallon tank.

That means that a full 20 lb propane tank contains 4.6 gallons x 91,452 BTU = 420,679 BTU of energy.

When calculating how long does a propane tank last on a patio heater, we need to take the efficiency of the patio heater into account. A good estimate is that patio heaters have 90% efficiency.

That means that the useful energy, available for heating, is:

Useful Energy = 420,679 BTU × 0.9 = 378,611 BTU

Now that we know how much energy does a propane patio heater’s tank hold, let’s look at how the heating output of patio heaters determines how long will a patio heater last:

How Long Does A Patio Heater Tank Last For 10,000 BTU – 50,000 BTU Units?

We know that 20 lb holds 378,611 BTU of useful energy. A 10,000 BTU patio heater burns through 10,000 BTU worth of propane every hour. A 50,000 BTU patio heater uses 50,000 BTU worth of propane every hour.

Example: We can quite easily calculate how long will a 30,000 BTU patio heater last on a 20 lb propane tank like this;

30,000 BTU patio heater time = 378,611 BTU / 30,000 BTU per hour = 12.62 hours

In short, a propane tank for a 30,000 BTU outdoor patio heater lasts for 12 hours and 37 minutes.

We can calculate this time for patio heaters of any BTU capacity. That’s exactly what we did and summarized the results in this table:

You can check out what is the BTU output of your patio heater and use this table to check how long will the propane tank last.

If you have any questions regarding calculations, you can pose a question in the comments below and we’ll be happy to help you out.