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

My first time looking at and measuring a DX/evaporator coil was pretty intimidating. The first one I encountered had four circuits (two intertwined and two face-split) and looked like it had a thousand capillary tubes. To make things more challenging, the coil was installed at an angle. But in reality, DX/evaporator coils aren't much more complex than other types of coils. They just have distributors that need to be considered during the measurement process. Still, I wasn’t sure how I would price this unit competitively.

There are several techniques you can use to ensure accurate coil sizing, as well as additional data from your clients that can optimize performance. A coil schedule—essentially a chart that provides estimated performance and capacities based on input specifications—can be very useful, especially when dealing with space constraints. This data is also helpful during the quoting process.

Although we often visit a site only once per job for the client's convenience, there are times when we measure coils for budget pricing and know we'll return later for more details. For these situations, especially when measuring multiple varying DX/evaporator coil sizes, there are a few variables you can always rely on for quick and accurate pricing to the customer.

Before we start, get a free blank coil worksheet to record your measurements.

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

2. Measure the finned length next, either at the top or bottom of the coil near the flanges (not in the middle). Make sure the tape measure starts and ends inside the end flanges.

While on the face, I’d also 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. One of the most critical factors in accurately pricing any coil is the copper tube size (3/8”, 1/2”, 5/8”) and the number of rows.

Depending on the face area of a coil, over- or under-counting the number of rows can result in thousands of dollars difference in an estimate. When I have access to the end of the coil that exposes its u-bends, I count the rows by determining how many tubes come out of the end plate from left to right. This can sometimes be confused with the number of u-bends, as two u-bends might actually equal four rows. The number of circuits will also affect pricing, and this can be determined simply by counting the returns or distributors you see.

If you have access to all the above measurements, you’re set to get an accurate cost without worrying about factors that could increase your cost and impact profits. Sometimes, you’ll need to improvise, and that’s when it can be crucial to learn what additional performance information the building can provide. For instance, 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. So, I might take the casing depth of the coil (say 5") and the capacity of the connected condensing unit (say 30 tons). If I can figure out the CFM the air handler is running, even better (or I can estimate around 350-400 CFM per ton). I would plug this data in to determine the maximum number of ½" rows (if the copper tube size is ½") that can fit inside a 5" casing depth. The selection should ideally bring back a capacity close to the 30 tons we're aiming for, then I can begin quoting and consulting with the customer.

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