4 Easy Steps to Size Gas Pipe

Are you engaged in a natural gas project? Are you experiencing flow or pressure problems in your gas installation?

Either of these scenarios requires you to determine how to size the gas line. Learning your gas line size can help eliminate low pressure, inefficient flow, and wasted energy.

There is a basic formula for gas pipe sizing, ensuring that your installation is efficient and reliable, whether you use it in a domestic or commercial setting.

In this article, I will explain how you can size gas lines and the important factors to consider in the process to ensure that the gas line can supply all connected appliances with enough gas for consumption.

So let’s jump in!

Table of Contents

The importance of correct gas sizing

Not every pipe can be used in a gas supply system. Using the right size pipe ensures the safety and efficiency of the entire application.

Pipe size determines how much gas can pass through the pipe and reach the receiving application. Longer pipes may seem ideal, but excessive length can result in a lower volumetric flow rate of gas, measured in British thermal units (BTUs) per hour. Knowing the dimensions of gas pipes, including diameter and length, helps you understand how much gas can pass through the pipe system.

As a general rule, for a gas piping system to work efficiently, the pressure loss should not be greater than the difference between the starting pressure at the gas meter and the pressure at the appliance.

Sizing variables of gas pipelines

Several factors come into play when determining gas line size. A basic understanding of these variables will help you calculate and determine the right pipe size for your natural gas installation.

Nominal size

The nominal size of the gas pipe refers to the outside dimension, which generally serves as a reference point when sizing the pipe for gas systems. The inside size of the pipe is usually smaller. For example, a pipe with a nominal size of 2 inches will have an internal dimension of slightly less than one inch.

Pipe length

The length of the pipe plays an important role in determining how much gas flows through the pipe. The longer the pipe, the lower the gas pressure. But, you also need to take into account the nominal size of the pipe. Smaller nominal pipe size may limit pressure flow. The big pipe offers more pressure, but comes with concerns about profitability.

Application

Generally, the gas line is nominally about four inches in size, but it is common for some gas systems to use 8-inch lines. The exact size of the gas line will vary from application to application. Smaller gas systems may need piping with a smaller nominal size to allow the piping to carry the gas directly to a particular appliance. This pipe will also likely be shorter due to the size of the application being used. Larger gas systems serving multiple applications will require longer piping with a slightly larger nominal size to provide the desired pressure at the point of the appliance.

Pipe type

The material of the pipe greatly influences the amount of BTUs the gas pipe system can deliver to the appliance.

The type of pipe you use will depend on your building codes, but copper and steel pipe are the most common. Polyethylene and PVC pipes can be applied in outdoor and underground pipeline gas systems. Depending on the application, you can also use other pipe materials such as iron, brass and aluminum.

Step by step guide on how to size gas pipe

Now that we’ve explored the basic variables that influence gas pipe size and gas system efficiency, let’s look at how to size pipe for safety and efficiency.

Step 1: Consider the number of appliances that require gas

When installing a natural gas system, you must consider the number of appliances you will include in the system to receive gas. The number of appliances to be serviced will influence the pipe length and nominal size.

For example, will the gas system serve only one boiler, or will the installation include additional appliances such as the stove and a cooling and heating system? These considerations will influence the size of the pipe.

Step 2: Determine the mechanical requirements of the appliances

In addition to efficiency and cost effectiveness, safety should be your top priority when determining the right pipe size for your gas system installation.

Matching the size and type of pipe to the mechanical and technical requirements of the appliance can help ensure the safety and integrity of the gas system.

In terms of technical and mechanical requirements, the most important details to look out for are the inlet pressure of each appliance and the flow rate.

Pro tip: It helps you draw your piping system to help you visualize the installation process and determine the amount of pipes and fittings you need. The layout should start at the gas meter point and include all appliances that require gas.

Step 3: Determine the pipe size

Longest length is the most common method of pipe sizing. The method involves determining the longest length of pipe from the delivery point, regulator or gas meter to the farthest appliance on the system. This length is known as the index length.

When determining the index length, you should consider possible pressure loss from fittings and elbows. The basic formula for accounting for pressure loss is to add 20% of the original index length to this figure.

For example, if the length from the gas meter to the farthest device on the system is 35 m, the length of the estimated index after adding the 20% will be 42 m, i.e. 35+ (35×0.2).

Step 4: Refer to the gas system sizing chart

Get a commonly used sizing chart to help you determine the correct pipe size (in terms of nominal diameter) you’ll need based on BTU (flow rate) and pipe length.

Use the length of the index as a reference point and the combined BTUs of the appliances in the system. Then use the table to identify the pipe length equal to or greater than the index length.

Next, look at the throughput requirements (BTUs) of each appliance. The table identifies the BTU value equal to or greater than BTU for each appliance. Next, check the appropriate pipe size.

When using the Longest Length method for sizing gas piping, some factors to consider are building height, different pressure requirements, and type of appliances.

The additional height will affect variables such as pipe length and pressure requirements if you are doing a gas pipe installation in a very tall building.

Appliances in your gas system may have different pressure requirements. This is normal and nothing to worry about. But when sizing the gas line, use the highest pressure requirements in the calculation.

Finally, even if you have several appliances in your gas piping system, they will not all work at the same time. As such, it is not necessary to activate the 100% request.

Calculating pipe diameter using volumetric flow requirements

As a general rule, process engineers recommend a velocity of 90-100 feet per second of gas flowing through the pipeline. You can use this standard to determine the correct pipe diameter size.

To complete the calculation, you should find out the required de total volumetric flow rate of each appliance on the gas piping system. This information is usually indicated on the device.

So let’s say the required volumetric flow rate is 110,000 cubic feet per hour at 190 psi (pounds per square inch).

To determine pipe diameter, use industry recommended velocity and volumetric flow rate. The recommended velocity of gas through the pipeline is 90-100 feet per second, so let’s use an average of 95 feet per second.

First, convert the recommended speed from feet per second to feet per hour. To do this, multiply the recommended speed of 95 by 3,600 seconds (equivalent to one hour). The result is 342,000 feet per hour.

Next, find the nominal diameter of the pipe by dividing the volumetric flow requirements of the appliances (110,000 cubic feet per hour) by the velocity, which is 110,000 divided by 342,000. The result is 0.29 square feet, which is the diameter of the pipe.

Summary: How to size the gas pipe

Determining the correct gas line size is the first step in ensuring an efficient, effective, safe natural gas system installation. The longest length method is most commonly used when sizing gas piping for a multi-appliance system. With a single appliance, you can calculate the nominal diameter using the industry recommended velocity value and the volumetric flow rates of the appliance for simple systems.