What Makes a Coil Custom?

Colby Maun • June 22, 2026

What exactly makes a custom coil custom? Most facility managers assume that a custom coil only differs from OEM in sizing. The reality is that dimensions are only a fraction of what makes a custom coil custom. Each job is different, with many different factors going into a custom coil, such as dimensions, tube configuration, fin design, materials, and performance requirements.

The most commonly thought of aspect when it comes to custom coils is the dimensions. This includes height, width, and depth of the coil, which allows for custom replacement coils to fit perfectly into the system they are designed for. Doing this without major modifications is crucial when manufacturing a custom replacement coil.

The tube configuration of the coil also plays a very important role in customization. The circuitry, number of rows, and tube diameter all impact this aspect and contribute to the efficiency and heat transfer of a custom coil.

Fin design affects the airflow and heat transfer efficiency of a custom coil, which is very specific for each job. Fin types can be straight, corrugated, louvered, or ripple. A straight fin type is the simplest design and is easier to clean, which makes it more suited for industrial environments and dirty facilities. Corrugated fins are wavy in pattern and transfer heat better than straight fins, making them good for rooftop units and air handlers. Louvered fins contain small, angled cuts and work best in high-performance and energy-efficient systems. The specific spacing of the fins matters as well, since each job contains different airflow and pressure drop requirements.

Another factor that must be taken into account for a custom coil is the material the coil is manufactured with. Custom coils can be made with copper, galvanized steel, stainless steel, aluminum, cupronickel, and more. Copper is traditionally the industry standard for tubing; however, it can also be found rarely in the fins. Copper transfers heat very efficiently and is very easy to repair, but this comes with higher costs and corrosion concerns. Galvanized steel is most common in the case of the coil, since it is durable and affordable, yet it faces shorter lifespans in harsh environments. Stainless steel is an option for tubing, fins, and casing, and is commonly selected for its durability and corrosion-resistant nature. It’s often one of the more expensive options and does not transfer heat as well as other materials. Aluminum is the most common material for the fins in a coil and is often chosen for its inexpensive and lightweight properties. For fin purposes, it is ideal, yet for tubing and casing purposes, it can be more difficult to repair and more susceptible to physical damage. Cupronickel is only used for the tubes and is the premium corrosion-resistant option. It is very expensive, which puts it behind copper in terms of commonality.

The final factor that goes into a custom coil is the performance requirements that each job entails. Pressure drop, operating temperatures, capacity, and airflow all differ based on the requirements of the job. When it comes to performance requirements, flow rate is one of the most important elements. Flow rate is the volume of air or fluid moving through the coil, and having a flow rate that is too high or too low results in inefficiency and lower coil performance. Which type of refrigerant the coil uses impacts customization since different refrigerants behave differently. With the new refrigerant guidelines shifting coils towards R-454B and R-32, custom coils need to be manufactured to handle these refrigerants.

At HeatEX Technologies, we carefully consider each of these factors to make sure that every coil replacement is engineered for the specific job and system. Specializing in a wide variety of coils and jobs, we understand that successful custom coil replacement accounts for performance, not just size. Explore our website for more information on how we can assist with your next replacement job.

Works Cited

KCL Systems. What Is a Custom Coil in HVAC? Behind the Scenes of Precision Coil Fabrication. KCL Systems, https://kclsystems.com/what-is-a-custom-coil-in-hvac-behind-the-scenes-of-precision-coil-fabrication/.

CFM Distributors. How Do You Select and Design a Custom Coil Replacement? CFM Distributors, https://rc.cfmdistributors.com/helpful-tips/how-do-you-select-and-design-a-custom-coil-replacement/.

Precision Coils. Coil Dimension Guidelines. Precision Coils, https://www.precision-coils.com/resources/coil-dimension-guidelines/.

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