In our previous post, we covered how to accurately measure a DX evaporator coil for pricing. Now that you’ve secured the job and the replacement coil is on its way, it's time to focus on the details that make all the difference—ensuring a perfect fit and hassle-free installation.

The casing depth, headers, distributor locations, and return connection points are all critical measurements. Getting these right ensures the coil will fit perfectly in the unit and function as intended.

Start by measuring the casing depth. This is the distance from the outside edge of the casing on one side to the other, from the entering air side to the leaving air side. This dimension is crucial because the casing often fills the entire space in the unit, and there may be no room for adjustment.

Measuring the casing depth

I also like to double-check the total available depth inside the coil section. This helps if the customer later decides to upgrade or downgrade the system’s capacity, allowing for more or fewer rows to be used.

Next, measure the casing height. I do this in two ways: first, by measuring from the top edge of the top flange to the bottom edge of the bottom flange. Second, by adding the height of each flange to the finned portion. Be sure the flanges are standard stacking types, not inverted or knife-edged, which can complicate things. If they’re non-standard, just note the total height, as flanges can usually be adjusted later.

Now, measure the casing length. This is the distance from the edge of the vertical flange near your supply and return connections to the edge of the opposite flange that covers the copper U-bends.

Measuring the casing length

Don’t forget the overall length (OAL). To get this, take three key measurements:

1. C Dimension: Measure from the end of the fin pack to the end of the return header.

2. Fin Length: Measure at the top or bottom of the coil, near the flanges—not in the middle. Make sure the tape starts and ends inside the end flanges.

3. Add the fin length to the MAX dimension: That’s the distance from the end of the fin pack to the outside of the U-bend on the other end of the coil.

The sum of these gives you the overall length of the coil—including headers but not including the return connection, which often extends beyond the unit. I always check the total available length in the unit to confirm my OAL and see if there's extra space if needed.

When it comes to circuiting, every detail matters. Be sure to record:

• The number of circuits
• The number of feeds per circuit
• The number of capillary tubes per circuit

Also, count the number of tubes from top to bottom in one row. This can help verify the finned height if needed.

Even though some coils are re-piped by installers, it’s best to keep the original return connection and distributor locations intact if possible.

Record the following:

• The distance from the bottom of the casing to the center of each connection point
• The distance from the connection to either face of the coil
• The distance in or out from the end of the fin pack

For dual-circuited coils, you can back up your measurements by checking the center-to-center distance between the two connections. Also, measure the diameter of the sweat return connection.

Once all these details are verified, the coil should match the specifications exactly. In some cases, adjustments like fins per inch, number of feeds, or circuits can affect the capacity without changing the construction. At this stage, it’s about finding the best solution for the customer’s needs.

If this all sounds like something best left to the pros, you're right! Contact me directly, and Nationwide Coils will provide accurate, professional measurements for your coil—so you can focus on what you do best.