The purpose of this article is to give you some general knowledge about the sizing of gas lines for your gas fire pit or fire table. Your licensed gas installer will evaluate your goals to determine the exact piping requirements for your situation. But a little knowledge will help you understand what they are proposing and any limitations you may encounter.
Why does my neighbor’s fire pit produce big flames and mine doesn’t?
We hear this question a lot: “My neighbor across the street and I have natural gas fire pits. Why does he have large, roaring flames and I can’t get mine to go above 6 inches?”
There could be many reasons for this. The most common reason is that your regulator isn’t supplying sufficient pressure, so you should check this first. For more details on this, check out our article, “Everything You Need to Know About Gas Regulators for Outdoor Fire Pits“.
If it’s not the regulator, it could be that the gas line feeding his outdoor area is larger in diameter than yours. If your line was sized for a gas grill, it may not be sufficient to add on a roaring fire pit. This may be remedied with regulators. Your gas professional can determine this.
It’s also possible that your neighbor’s gas supply doesn’t have to travel as far —only 10 feet from the house to the fire pit, as opposed to the 30 feet yours has to travel.
Perhaps the path of your pipeline requires more bends in the line to reach its destination. Each twist and turn slows the gas flow. To allow for the toll these turns take on your capacity, mentally add 5 feet of pipe to your total length for each occurrence. For instance, if you have 3 bends in your pipe, add 15 feet to total length when calculating your BTU/hr. output.
Effects of Pipe Diameter and Length
The following tables provide a quick example of the flow capacity of typical pipe sizes and lengths. These numbers are only for quick reference and should not be used to calculate the pipe size needed for your installation. They do not account for couplers or the bends and turns in your pipe. (Your gas specialist will be able to calculate the gas pipe size needed for your installation based on the design.)
The first column in the following tables show the distance the pipe will travel (Pipe Length). At the top of the next three columns is the inside diameter of the gas pipe. The rest of the numbers reflect how many BTU of gas can flow through that particular pipe length and diameter.
Typical Natural Gas Throughput at 3.5″ Water Column (WC) in BTUs
|Pipe Length||1/2″ Pipe||3/4″ Pipe||1” Pipe|
|10 ft.||162,000 BTU||530,000 BTU||1,220,000 BTU|
|20 ft.||114,000 BTU||375,000 BTU||863,000 BTU|
|30 ft.||94,000 BTU||306,000 BTU||704,000 BTU|
|40 ft.||81,000 BTU||265,000 BTU||610,000 BTU|
|60 ft.||66,000 BTU||216,000 BTU||498,000 BTU|
Using the table above as an example, if you have a 10-foot length of pipe that is ½” in diameter, it will provide 162,000 BTU/hr. of fire power (at a gas pressure of 3.5” WC).
Using the same example, 20 ft. of the same pipe produces only 114,000 BTU/hr. As you follow down the column (as the pipe gets longer and longer), you will see that the number of BTU decreases the further down you go.
You can also see from the chart that increasing the diameter size of the pipe greatly increases the BTU/hr. rate.
These properties hold true in the following chart of propane output. Regardless of the diameter size, the longer the pipe gets, the less BTU/hr. Whereas, a larger diameter of pipe greatly increases the BTU/hr. rate.
Typical Propane Gas Throughput at 3.5″ Water Column (WC) in BTUs
|Pipe Length||1/2″ Pipe||3/4″ Pipe||1” Pipe|
|10 ft.||263,000 BTU||860,000 BTU||2,500,000 BTU|
|20 ft.||186,000 BTU||608,000 BTU||1,400,000 BTU|
|30 ft.||152,000 BTU||498,000 BTU||1,140,000 BTU|
|40 ft.||131,000 BTU||430,000 BTU||990,000 BTU|
|60 ft.||108,000 BTU||350,000 BTU||807,000 BTU|
Why do I need a larger pipe diameter for natural gas?
The bottom line is this, it takes less propane gas to get the same BTU/hr. (heat value) as natural gas. For example, if you have two equal flames burning side by side—one produced by propane and one by natural gas—it will take 2.5 times more natural gas to produce the same amount of heat and flame size as the propane. Therefore, natural gas requires a larger diameter pipe size.
DID YOU KNOW that 1 cubic foot of natural gas provides 1,000 BTU/hr of heat, while the same amount of propane provides 2,500 BTU/hr ?
Why should I consider a larger pipe size in new construction?
It’s helpful to understand how pipe size and design affect output. When you’re talking with your gas installer about new construction, it’s a good idea to spec out a pipe size that can handle any future projects you might want such as a complete outdoor kitchen and multiple fire features.
It doesn’t cost much more to “overbuild” this aspect of your outdoor area, and it might save you a lot of headaches and money down the road.
Is My Existing Gas Feed Sufficient?
Most of our customers find their current installations are sufficient to support a gas grill and a fire pit, but that depends on several factors including the BTU rating of the burner. It’s a good idea to ask your gas installer to check the gas flow to make sure it’s sufficient to handle the intended BTU rating of your project.
If the flow will only support a moderate flame height with a 200,000 BTU/hr. burner, it might be worth considering a lower BTU rating (like 90,000 BTU/hr.) to get higher flames. Otherwise, you may have to forfeit full performance or tear up your existing hardscape to install a larger pipe size.
What do I need to discuss with my gas pipe installer?
This article gives you some basic understanding of pipe sizes and their effect. It is intended to give you a background so you can speak knowledgeably with your licensed gas installer and make informed decisions. It is not a substitute for using the services of a licensed gas professional.
Always use a professional for installation. They can properly assess your needs and make sure you have the proper equipment for safe and optimal performance.
If you still aren’t sure what questions to ask of your gas professional, feel free to contact us. We’re always happy to help.