Specifying a replacement coil for a process heating system doesn’t have to be intimidating. By following a few basic steps, you can obtain precise measurements for a custom-built coil.

Every day, hundreds of steam, water, condenser and evaporator coils fail due to old age or poor maintenance. If you’ve planned ahead or are simply lucky, you might have replacement coils on hand. But what happens if you don’t? How can you find a replacement for a coil that was installed decades ago if no identifying information (part number, serial number or manufacturer name) exists on the coil?

Fortunately, if you have the exact physical measurements of your existing coils, you can have a replacement coil custom-built for you. You can obtain these measurements by following a simple step-by-step procedure. You need only a few basic tools, including a tape measure, a tube size measurement tool (if available), a specific coil spec sheet (if available) and a digital camera (if available). To measure, follow these steps:
  1. Determine the type of coil - chilled water, evaporator, condenser, steam, hot water or other.

  2. Measure the diameter of the tubes (these run directly one above the other from bottom to top) with a coil measuring tool or tape measure. The tube diameter typically measures 0.375, 0.5, 0.625 or 1".

  3. Count the number of rows deep. Chilled water and direct expansion coils have anywhere from one to 10 rows, and condenser coils have anywhere from one to six rows. Steam or hot water coils typically have two rows.

  4. Count the number of fins per inch using a coil measuring tool or tape measure. This number typically ranges between four and 16.

  5. Measure the height and length of the fins. These measurements, which are typically abbreviated in specifications to FH and FL, respectively, are the actual open area of the coil that the air passes over.

  6. Measure the envelope dimension of the coil. The envelope includes the overall casing height (CH), casing length (CL) and casing diameter (CD).

  7. Measure the overall length of the coil (OLH), including return bends and manifolds. Do not include the length of connection stubs.

  8. Measure the connection sizes using a coil measurement tool or tape measure. Connections are usually a male pipe thread (MPT) or female pipe thread (FPT).
Once you have obtained all of the basic measurements, you can submit your specification to a coil manufacturer to obtain a custom-built coil. Always carefully review your specification before submitting it to ensure that the information is accurate. You should also provide a photo of the old coil whenever possible for additional verification.

By following these basic steps, you can easily replace your failed coils and get your process back up and running again quickly.