By J. Herwick
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Looking to avoid running out of fire pit propane at your next backyard gathering? Knowing your fire pit's propane fuel consumption rate, along with the size propane tank you have, can save you from experiencing this embarrassing situation. Once you've got that information ID'd, figuring out how long a fire pit propane tank will last is a snap.
I'll cover that and more further down, but for those who can't wait and want an answer right now on how long that fire pit propane tank will hold out at your next fire, this is for you.
Generally speaking, a typical 50,000 BTU propane fire pit, for example, equipped with a standard 20 lb. propane tank, will burn for approximately 7 hours at its highest setting. Estimated fire pit propane tank burn time is calculated as follows: Total Propane Tank BTUs, divided by Fire Pit BTU rating, times an average propane burning efficiency of 85%.
This estimate is based on an average gas fire pit BTU rating and may not match up with your particular model's design and or current condition.
Check out the owner's manual of the fire pit you own or have in mind for a more precise estimate of propane consumption rates.
I'll get into the specifics of total propane tank BTUs, fire pit BTU ratings, propane burning efficiency, etc., in a little more detail below.
I've also got you covered with a calculator further down that will give you an estimate of how long a fire pit propane tank last if you don't feel like doing the calculations manually, as I'll show you how to do next.
How Quickly Does a Fire Pit Burn Propane?
To understand how long your fire pit's propane tank is going to last, you need to understand how quickly your gas fire pit burns gas over time. Before I get into that, I want to cover BTUs, what they are, why they matter, etc., for a second.
Propane fire pits typically come with what is called a BTU rating.
Without going into a lot of the science about it, this rating basically represents the amount of heat energy a propane (or natural gas) fire pit puts out in one hour.
The higher a fire pit's BTU rating, the more heat is produced per hour.
Naturally, with a higher BTU rating, is (30,000 BTU, 50,000 BTU, 75,000, etc.), the more propane your gas fire pit is going to use.
If you look back at the 50,000 BTU fire pit example at the beginning of the article, you'll see that I wrote that it takes about 7 hours to burn through a full 20 lb. propane tank.
Let me show you how I came up with that burn time.
How to Calculate Fire Pit Propane Consumption
To determine how long a fire pit will run on a tank of propane we'll have to gather a little information about fire pit propane tank sizes, the number of propane BTUs by tank size, the fire pit's BTU rating, etc., and then do the calculation.
If you are not a math ninja don't sweat it, I'm not one either. I promise to make this as easy as possible.
Fire Pit Propane “Fast Facts”
– Propane naturally has no smell; the rotten-egg smell associated with propane comes from an additive included for safety reasons
– Propane is a byproduct of gasoline evaporation
– The U.S. produces almost 90% of the world's propane, with Canada and Mexico producing the rest
– Propane can only burn at extremely high temperatures; it has to reach a temperature of 920° F before it ignites
Molecular Formula of Propane: C₃H₈
Propane Weight per Gallon (at 60° F): 4.23 lbs.
Propane Gallons per Pound: .236 gals.
British Thermal Units (BTUs) per Gallon of Propane: 91,502 BTUs
British Thermal Units (BTUs) per Pound of Propane: 21,548 BTUs
References: berico.com and amerigas.com
With that said, if you want to skip this altogether, check out my handy propane consumption calculator below.
Let's get into it with the first step by ID'ing the size of the fire pit propane tank you will be using. The smaller propane tanks or bottles below are typically used with more portable propane fire pits when weight and space are at a premium on the road or back home on a balcony.
Standard Propane Tank Sizes Used for Fire Pits
20# Propane Tank
Propane BTUs (full) 420,909 BTUs
Propane BTUs (75% full) 320,257 BTUs
Propane gals. (full) 4.6 gals.
Propane gals. (75% full) 3.5 gals.
11# Propane Tank
Propane BTUs (full) 237,905 BTUs
Propane BTUs (75% full) 173,854 BTUs
Propane gals. (full): 2.6 gals.
Propane gals. (75% full) 1.9 gals.
5# Propane Tank
Propane BTUs (full): 109,802 BTUs
Propane BTUs (75% full) 82,352 BTUs
Propane gals. (full) 1.2 gals.
Propane gals. (75% full) 0.9 gals.
1# Propane Bottle
Propane BTUs (full) 21,960 BTUs
Propane BTUs (75% full) 16,470 BTUs
Propane gals. (full) 24 gals.
Propane gals. (75% full) .18 gals.
Note: Most propane tanks are filled to about 75 to 80% capacity; use the numbers in light blue for greater accuracy when estimating how long your fire pit propane tank will last.
Steps for Calculating How Long a Fire Pit Propane Tank Will Last:
1. Identify what size fire pit propane tank you will be using
As I mentioned before, 20 lb. propane tanks (sometimes written as 20#) are the average propane tank size in the U.S. for fire pits, but other sizes can be and are used for a variety of reasons (i.e. 10, 5, and 1 lb. propane tanks).
Use the chart tank size chart above to figure out what size tank you will be using for your fire pit.
2. Calculate total fire pit propane BTUs
In order to understand how long your tank will last, you'll need to know the total number of BTUs your full propane tank is able to support.
For example, a full 20 lb. propane tank contains 4.6 gallons of propane. Each gallon of propane represents 91,502 BTUs. Or does it?
***IMPORTANT: This is where the calculation takes a slight turn and gets “interesting.” You may know this already if you are an experienced griller, propane fire pit user, or work in the propane industry.
—> Propane tanks are normally only filled up to around 75 to 80% capacity. They are never really full. <—
What does that mean exactly? It means we are going to calculate the amount of propane BTUs per tank at 75% capacity (see the figures in light blue in the propane tank chart above) to make sure you don't run out unexpectedly.
Instead of the normal 4.6-gallon capacity of a 20 lb. propane tank, the capacity we are going to use is 3.5 gallons (4.6 gallons x .75 = 3.45, or 3.5 gallons).
Multiply 3.5 (the number of gallons in a 20 lb. tank at 75% capacity) x 91,502 (the number of BTUs represented by a gallon of propane), and you'll get 320,257 BTUs.
3. Calculate the hours a fire pit propane tank will last
Now that you know the number of BTUs you have to work within your fire pit's propane tank, you will divide that number by your fire pit's BTU rating to figure out the total tank burn time; 320,257 (propane tank BTUs) ÷ 50,000 (fire pit BTU rating from example), and you would get 6.405, or 6.4 hours of burn time.
4. Calculate the total hours the fire pit propane tank will last (using propane efficiency)
We're almost there, but we need to account for propane fuel efficiency to really nail down the burn time number.
To do this, we use the EnergyStar AFUE (Annual Fuel Utilization Efficiency) rating for propane-fueled furnaces with an average efficiency of around 85%.
Why use the efficiency of a propane-fueled furnace on a fire pit calculation?
It's as close a figure as we are going to get, as EnergyStar has not calculated an efficiency rating for propane fire pits.
Anyway, we then take the burn time from Step 3 (6.4 hrs.) and multiply it by the average propane furnace efficiency rating of 85%, and we get 5.44, or 5.4 hrs.
This calculation (using the AFUE efficiency rating) is often left out of the equation when people are trying to figure out how long their fire pit propane tank will last.
Taking the time to do it should prevent any surprise runs to your local propane tank exchange when you least feel like doing it.
There is a little bit to it, and if you don't feel like doing the “back of the napkin” calculations in the future, check out the calculator below to speed up the process when using fire pits with different BTU ratings and other tank sizes.
Fire Pit Propane Tank Burn-time Calculator
How Do I Get More Time From a Tank of Propane?
This one is not too hard. Just turn your gas fire pit down to a lower setting to get more time out of a propane tank.
Fire pit settings are commonly just HIGH, LOW, and OFF. We've been calculating for the highest setting so far.
Theoretically, a LOW setting should get you around 25% to 40% percent more time on a propane tank, maybe more.
I'd guess it would likely vary from fire pit model to fire pit model, even those with like BTU ratings. Experimentation with lower settings would definitely be in order if you are looking to extend propane tank burn time
This is something that a manufacturer may be able to provide but I haven't seen any data yet included with any gas fire pit I've worked with.
Wrap-up: How Long Will a Fire Pit Propane Tank Last?
We hope that this article was helpful and gave you a better understanding of what goes into calculating the burn time of your fire pit's propane tank, how to do it, and how to make a propane tank last longer.
Have any tips or tricks that we didn’t mention? Drop me a line to let me know and I'll add it to the post. And don’t forget to share this post with your friends and family – they may find it helpful too!
Thanks again for reading, I hope you found the post useful.