How Do Gas Fire Pits Work?
Have you ever asked yourself, ‘How do gas fire pits work?’ if so, we’re here to fill in the blanks for you.
On an elementary level, how gas fire pits work is fairly simple. Essentially, a fuel source (such as natural gas or propane) supplies fuel, which is delivered through pipework (typically a hard pipe or feed pipe) to the fire pit location. The fuel ultimately reaches a burner, within the structure or enclosure, for ignition.
The 3 Main Elements of a Fire Pit
- The Fire Pit Gas Supply.
- The Fire Pit Gas Pipeline – from the fuel source to the fire pit.
- The Fire Pit Burner.
The Fire Pit Gas Supply
Typically there are three ways to supply gas to your fire pit project:
- Natural Gas supply via a meter into your property.
- Large Liquid Propane tank on your property.
- Small Liquid Propane tank (20 – 100 lbs).
Let’s take a closer look at the different types of gas supply and how gas fire pits work with each option.
Natural Gas Supply
In this case, your property is connected to the gas grid, which supplies fuel to your meter. The capacity of the meter, measured in cubic feet per hour (C.F.H.), is determined by your contract and was selected to meet your property’s gas needs at the time of installation.
For instance, if your gas contract and meter allow a maximum of 500,000 BTUs per hour, and your household appliances consume 350,000 BTUs per hour, you would have a spare capacity of 150,000 BTUs per hour. This surplus could be used for additional projects, such as installing a fire pit. projects, such as installing a fire pit
Important: Many assume that not all their appliances will run simultaneously, leading them to believe they have more gas available than this calculation suggests. While, theoretically, that may be true, U.S. Gas Codes require that these calculations consider all appliances running simultaneously. Failure to comply is not a road you would want to go down!
At this point, we’ve established that you have 150,000 BTUs per hour of spare capacity for your fire pit.
We cannot over-emphasize how critical it is to verify this figure. We strongly recommend having a Gas Technician come to your property to perform the necessary calculations. Alternatively, your gas supplier may be able to provide insights into your system’s available capacity, so it’s worth giving them a call. In some cases, they may even increase your supply—often at no extra cost.
Large Liquid Propane Storage Tank
If you have a large liquid propane tank on site, establishing how much surplus gas supply you have from the tank still applies.
A 500-gallon “whole house” propane tank holds 400 gallons when full (80%) which is 36,600,000 BTUs. As there are no pressure, or flow rate restrictions as with a metered Natural Gas supply, it is unlikely that you will run into a gas supply issue.
Large LP tanks operate at a much higher pressure than small 20 lb tanks and require two-stage regulators to reduce the pressure to ‘domestic levels.’
As always, we highly recommend using the services of a qualified Gas Technician when connecting any appliance to an LP storage tank system.
Small Liquid Propane Tank
If you don’t have access to a large propane storage tank or natural gas supply, smaller propane bottles ranging from 20 lbs to 100 lbs are a great option.
The 20 lb propane bottle is commonly used with outdoor grills, but there are limitations when connecting to larger appliances like fire pits.
Most standard regulators used to connect to appliances have a built-in flow rate restrictor designed to prevent over-pressurization. These restrictors automatically cut off the gas supply if they detect a flow rate higher than approximately 100,000 BTUs per hour (it’s best to stay below 90,000 BTUs), which could be interpreted as a gas leak – leading to your fire pit shutting off unexpectedly.
This means that when using smaller LP bottles (20 lbs to 100 lbs), you’re generally limited to burners rated at 90,000 BTUs per hour or less if you use standard regulators.
However, there’s a workaround to this limitation: use a UL Certified High Flow Regulator, which supports a flow rate of up to 175,000 BTUs per hour, allowing you to connect a burner rated up to 175,000 BTUs/hr.
Of course, the higher BTU-rated burners will empty your gas bottles much faster!
For example, a 20 lb propane tank contains about 430,000 BTUs. With a 90,000 BTU/hr burner, the tank will run for about 4 ¾ hours (430,000 ÷ 90,000). But with a high-flow regulator and a 140,000 BTU/hr burner, the same bottle would be emptied in 3 hours.
Propane Tank Holders
Some manufacturers offer decorative Propane Tank Holders, providing an excellent solution for concealing unsightly gas bottles.
When considering the location of the small gas bottle, testing has shown that a gas line longer than twelve feet between the bottle and the burner negatively affects the flame quality. Therefore, the maximum distance the bottle can be from the fire pit is approximately twelve feet.
Having discussed gas supply and calculated the actual figure of how much gas is available for your project, what’s next?
The Pipeline
It’s crucial to understand how gas fire pits work in relation to your gas supply.
Earlier, we had calculated as an example that there was a spare capacity of 150,000 BTUs that we could direct to our fire pit project.
It stands to reason that we want to get all of the gas to the fire pit location, which is why selecting the correct sized hard pipe is vital.
The hard pipe runs from where you tap into your gas supply (your large propane storage bottle or your natural gas household) to the inside of the fire pit structure. From there, a flexible gas line will connect it to the burner.
The critical factor here is the distance the gas travels through the hard pipe (actual distance traveled, not a straight-line measurement).
The NFPA (Nation Fire Protection Association) has published a Gas Code (NFPA 54), which includes two tables for calculating the hard pipe size for natural gas and propane setups. These are the go-to reference tables for gas professionals which we have published in our article Gas Hard Piping Size For Fire Pits.
Using our 150,000 BTU figure and natural gas as our example, if the hard pipe run is 20 feet, a 3/4 diameter pipe will deliver up to 160,000 BTUs/hour. So that would work for this example.
However, if the same 3/4-inch pipe run was 50 feet, the pipe can only deliver 98,000 BTUs, about two-thirds of what is required, if you had a 150,000 BTU-rated burner connected. This shortfall would seriously affect the size and quality of the flame.
It requires a 1-inch diameter pipe to move 150,000 BTUs/hour of natural gas over 50 feet.
In short, the more gas you need to move and the further it travels, the bigger the diameter of the hard/feed pipe you require.
Important. There are two reference tables, one for natural gas and one for propane, be sure to consult the correct tables, as the numbers differ.
Having got the gas to the fire pit structure via the hard pipe, we can now take a look at the burner.
The Burner
The range of burners on the market today is vast and varied. Our article the Best Fire Pit Burners For 2024 looks closely at the options available, and how they perform.
The design, features, or size of a burner are irrelevant to the question “How do gas fire pits work?”. We need only to look at one aspect of the burner, the BTU rating.
All gas fire pit burners, like other domestic gas appliances, have a BTU rating which tells us how much gas per hour the unit needs to perform optimally.
As we have already seen, insufficient gas supply can result in small flames to possibly virtually no flame, not a great result for all your hard work and investment.
When choosing which burner to install, it’s essential to consider everything you’ve read above. By knowing how many BTUs are available at the fire pit location and understanding how gas fire pits work, you’ll be able to select the right burner with a matching BTU rating, ensuring you achieve the fire pit of your dreams.
If your existing fire pit isn’t producing the flame size you hoped for, troubleshoot by:
- Verifying the burner’s BTU range matches the available gas supply.
- Confirming how much gas is being delivered to the fire pit.
- Ensuring the pipe size is adequate to deliver the required BTUs per hour for the burner.
Further Reading
For more information, please refer to our article How To Successfully Build A Gas Fire Pit which delves deeper into the process discussed here.
How do gas fire pits work – Resources: Propane Tanks Specifications