Measuring DX Evaporator Coils For Pricing: In the field with Chris Wright

My first time measuring a DX evaporator coil was a bit overwhelming. I remember looking at a 4-circuit coil (2 intertwined + 2 face split) that had what felt like a thousand capillary tubes, and it was even tilted on an angle. In reality, DX coils aren’t much more complex than other types of coils — they just have distributors that need to be considered during measurement. Still, I wasn't sure how to price it effectively.

There are several techniques to ensure accurate sizing, and additional data from clients can also help optimize performance. A coil schedule or any available performance data can be extremely helpful, especially when dealing with space constraints. This information is also useful during the quoting process.

Although we often visit a site only once per job for convenience, there are times when we measure coils for budget pricing and know we'll return later for more details. In these situations, especially when measuring multiple varying sizes of DX coils, there are certain variables that can always be counted on for quick and accurate pricing to the customer.

Before starting, download a free blank coil worksheet to record your measurements.

1. Measure the finned height, taking the measurement from the top to the bottom of the fins on one end of the coil (not in the middle of the face).

2. Next, measure the finned length on the face, either at the top or bottom near the flanges (not in the center). The tape measure should start and end inside the end flanges.

While on the face, take the fins per inch. You can do this by counting the number of fins between 2” and 3” on the tape from left to right.

3. A critical factor in accurate coil pricing is the copper tube size (3/8”, 1/2”, 5/8”) and the number of rows.

The number of rows can significantly impact the cost, sometimes by thousands of dollars. When I can access the end of the coil showing the u-bends, I count the rows by determining how many tubes come out of the end plate from left to right. This can be confusing because two u-bends may equal four rows. The number of circuits also affects pricing, which can be determined simply by counting the returns or distributors visible.

If you have access to all the above measurements, you’re well-prepared to get an accurate cost without worrying about factors that might increase costs and affect profits. Sometimes improvisation is necessary, and that’s when it becomes crucial to understand what additional performance information the building can provide. For example, if the u-bends on an evaporator coil are not visible from either end, you can use a combination of casing depth and condensing unit capacity to determine the number of rows. If the casing depth is 5" and the condensing unit is 30 tons, you can estimate the maximum number of ½" rows that fit in the casing. Using this data, you can aim for a capacity close to the 30 tons needed, then proceed with the quote and consult with the customer.

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