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How do gas fire pits work?

Building A Fire Pit
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How do gas fire pits work?

On an elementary level, a gas fire pit is a straightforward machine. Have you ever asked yourself, ‘How do gas fire pits work?’ if so, we’re here to fill in the blanks for you.

Essentially, you have a fuel source (Gas Supply) that supplies fuel through pipework (Hard Pipe/Feed Pipe) to the fire pit location and a burner secured within a structure.

The Three Main Elements of a Fire Pit

The three main elements that make up a gas fire pit are:

  1. The gas supply.
  2. The gas pipeline from its source to the fire pit.
  3. The burner.

The Gas Supply

Typically there are three ways to supply gas to your fire pit project:

  1. Natural Gas supply via a meter into your property.
  2. Large Liquid Propane tank on your property.
  3. Small Liquid Propane tank (20 – 100 lbs).

Let’s take a closer look at the different types of gas supply.

Natural Gas Supply

In this case, your property links to the grid, which feeds gas to your meter. The quantity of gas you can draw is not limitless. Just like your electricity contract, there is a maximum amount you can use.

Suppose your gas contract/meter allows you to draw a maximum of 500,000 BTUs per hour and that all your household appliances’ gas requirements total 350,000 BTUs. You can now calculate you currently have a spare capacity of 150,000 BTU per hour which can be used for your fire pit project.

Important: people often think that not all their appliances will run simultaneously and that they have more gas available than this calculation reveals.

Theoretically, that is probably correct, but US Gas Codes require that these calculations consider all appliances running simultaneously. Failure to comply is not a road you would want to go down!

We have now established that you have 150,000 BTUs per hour available that you can use for your fire pit.

We cannot over-emphasize how important it is to establish this figure. We recommend you get a Gas Technician to visit and make the calculations.

Alternatively, your gas supplier may be able to advise you on how much spare capacity your system has. It is definitely worth a phone call. It is also possible that they can increase your supply, and some companies will do that cost-free.

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.

However, a 250 lb propane storage tank has a total gas content of 18,300,000 BTUs and does not have the limit per hour restriction that a metered Natural gas supply has. So 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 an LP storage tank or an NG supply, you can consider the small LP tanks, ranging from 20 lbs up to 100 lbs.

How do gas fire pits work?

Typically the 20 lb version is usually seen connected to outdoor grills etc. However, some limitations apply when using these smaller bottles.

Using a Propane Regulator to connect your device to these small tanks is necessary. The downside is that standard regulators have a flow rate restrictor built-in.

These restrictors automatically cut off the gas supply if they detect a flow rate higher than 100,000 BTUs per hour (best to think about 90,000 BTU to be on the safe side); they believe it is a gas leak and so it shuts down, and your fire pit stops burning!

As a result, when using small LP gas bottles ranging from 20 – 100 lbs, all of which use the same type of regulator, you are limited to selecting burners rated at about 90,000 BTU per hour or less.

A 20 lb bottle holds 430,000 BTUs. When connected to a 90,000 BTU per hour burner, the bottle would empty in about 4 3/4 hours (430,000 divided by 90,000).

There is a workaround to this flow rate issue. We can supply a UL Certified Regulator with a flow rate of up to 175,000 BTUs/hour, which means you can connect this to a burner rated up to 175,000 BTUs/hour.

Of course, using this high-flow regulator will empty your gas bottles faster!

Propane Tank Holders

Some manufacturers make decorative Propane Tank Holders, providing an excellent way to hide an ugly gas bottle.

Also, when trying to hide a gas bottle, testing has shown that a regulator to burner gas line length over twelve feet is detrimental to the flame quality. Therefore the max distance the bottle can be from the fire pit is about 12 feet.

Having discussed what gas options are available and calculated the actual figure of how much gas is available for your project, what’s next?

The Pipeline

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.

Final Gas Connection to 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.

A diagram showing the increase in feed pipe size over distance

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 2023 looks closely at the options available, and how they perform.

For the purposes of answering the question “How do gas fire pits work?”, we are only interested in one aspect of the burner, not its design, features, or size. No, at this stage, we are only interested in the burners’ BTU rating.

All fire pit burners and domestic gas appliances have a BTU rating, which tells us how much gas per hour the unit needs to perform optimally.

In the case of fire pit burners, insufficient gas supply can result in small flames to possibly virtually no flame at all, not a great result for all your hard work and investment.

Therefore it is imperative when considering which burner to use that you know how much gas is getting delivered to the fire pit and select a burner whose BTU rating matches the amount of gas supplied to the fire pit.

If an existing fire pit is not producing the flame size you hoped for; you can use the concept described in this article to troubleshoot the issue:

  1. Calculate how much gas is available to your fire pit from the source
  2. Check the existing hard pipe is the correct size to move the amount of gas in 1.
  3. Select a burner within the BTU range of gas delivered to the fire pit.

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