How to Measure a Coil to Order a Marlo Replacement

Ordering a replacement coil is an in-depth process, but can be accomplished relatively easily if you use the tools we provide and follow the simple steps below. Your local Marlo Independent Manufacturer’s Representative will be happy to assist you with this process, and can enter the details about your coil into our MarloMetrics coil selection software to provide you with an immediate quote.

STEP 1: Get the Tools You Need

Before you begin, download and print out our Coil Measurement Tool and cut out the tube diameters with a scissors, or just contact your Independent Manufacturer’s Representative for a durable plastic version of the tool. Then download the appropriate Coil Order Form from the list at the bottom of our Downloads page.

You’ll also need a tape measure and a pencil or pen to write the coil measurements and information on the order form.

STEP 2: Measure and Count

To get started, you’ll simply need to take several measurements and counts from the coil you need to replace. Using the diagram at right (and on the Coil Measurement Tool) for reference, take each of the following measurements – and counts – and enter the values in the corresponding spaces on the coil order form. Default units are inches. If dimensions are provided in millimeters, be sure to specify and we will convert to the closest imperial sizes.

1. Tube diameter – the Coil Measurement Tool has semi-circular cutouts that can be used to determine the tube diameter
2. Fin height – see FH on the diagram
3. Fin length – see FL on the diagram
4. Number of fins per inch – examples are marked on the Coil Measurement Tool, or you can simply count the number of fins over 3 or 4 inches and divide by the number of inches
5. Casing length – see CL on the diagram
6. Casing height – see CH on the diagram
7. Casing depth – see CD on the diagram
8. Number of tube rows – count the number of tubes running horizontally across the coil, making sure not to miss any tubes that may be hidden by the coil headers
9. Number of tubes high – count the number of tubes running vertically from the top to the bottom of the coil (divide FH/1.5 for 5/8” tubes or FH/2.25 for 1” tubes)
10. Header clearance – this is the distance from the casing to the outside of the header tube (see HD on the diagram)
11. Connection length – measure the length of the header connection (see SL on the diagram)
12. Connection locations – two measurements are needed to identify the location of each connection (supply and return): the distance from the top or bottom edge of the casing to the center of the connection stub, and the distance from the side edge of the casing to the center of the connection stub. In the example used in the diagram, the return connection measurements are labeled O and R, while the supply connection measurements are labeled S and I. Note: the right and left sides of the coil are determined by looking at the coil in the direction of the airflow (facing the side where air enters the coil).
13. Flange width – measure the width of the “frame” of the casing (see RF and HF on the diagram). This value is equal to the difference between the overall casing length and the fin length.
14. Bottom & Top Flanges – measure the height of the Bottom Flange (see BF on diagram) and Top Flange (see TF on diagram)
15. Feeds – sometimes referred to as serpentine, this is the number of tubes that go into the supply and return header
16. Connection size and type – identify the diameter of the connection stub tube using the cutouts on the Coil Measurement Tool. Also determine the connection type (male threads, female threads, flanged or plain) and material (typically copper, brass, steel or stainless steel).

STEP 3: Determine Coil Configuration

Next, just answer these 5 simple questions about the coil’s configuration:

1. Does the coil have horizontal or vertical tubes?
2. Are the connections on the right or left side of the coil (while looking at the coil in the direction of the airflow).
3. Does the coil have a pitched or straight casing?
4. Is the airflow horizontal or vertical?
5. Does the coil have any modifications to the casing? If so, note them on the order form.

STEP 4: Determine Coil Type and Materials

Coil Type: Identify which of the following coil types you need: steam distributing, steam blast, heating (water, glycol or oil), cooling (water, glycol or refrigerant), or condensing (refrigerant). See examples here.

Materials: Identify the type of metal for each of the following: tubes, fins, casings, headers and connections. Typical materials include copper, steel, stainless steel, copper nickel and aluminum.

STEP 5: Identify any Required Performance Changes

While you may be ordering a coil that’s an exact replacement in size, it doesn’t have to be an exact replacement in performance. If you’re looking to improve the performance of your system, we’ll be happy to make the needed adjustments. Just discuss your needs with your Marlo representative or contact us with any questions.

System improvements we can achieve through coil design changes include things like increasing or decreasing the air temperature leaving the coil, and reducing air pressure drop to increase fan efficiency, resulting in lower energy usage. These are just two examples of how coil design can impact overall system performance. We’re always ready to work with you to customize your coil to meet your individual needs.

If these “simple steps” look a little intimidating, rest assured that there’s a coil expert in your area who is ready to measure and quote your coil, and make sure you get the exact replacement you need for your specific application. Click here and enter your zip code to find a Marlo reseller near you.