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

My first time looking at and attempting to measure a DX/evaporator coil was intimidating. One of the first DX coils I encountered was a 4-circuit (2 intertwined + 2 face split) with what seemed like a thousand capillary tubes; and on top of that, the coil sat at an angle. In reality, DX/evaporator coils are no more difficult than others to measure—they just include one or more distributors that need to be considered in the process. Still, I wasn’t sure how I’d price this thing competitively.

There are various techniques to ensure accurate coil sizing, as well as additional data we can gather from our clients to optimize performance. Having a coil schedule—a chart that gives estimated performance and capacities based on input specifications—or any available performance data can also be helpful when dealing with space restrictions. Plus, this information is useful during the quoting process as well.

Although we often only visit a site once per job for the client’s convenience, there are many instances where we’re measuring coils for budget pricing and know we’ll be able to return later for more details. For these budget situations, especially when measuring a large quantity of varying DX/evaporator coil sizes, there are several 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, taking it from the top to the bottom of the fins on one end of the coil—not from the middle of the coil face.

2. Next, measure the finned length on the face, either at the top or bottom of the coil near the flanges—not in the middle. The tape measure should start and end inside the end flanges.

While on the face, I’d also go ahead and get the fins per inch. You can do this by taking a pen and counting the number of fins between 2” and 3” on the tape from left to right.

3. Moving along, a critical factor in accurately pricing any coil is the copper tube size (3/8”, 1/2”, 5/8”) and the number of rows it has.

Depending on the face area of a coil, over- or under-counting on rows can make thousands of dollars difference in an estimate. When I have access to an 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 often be confused with the number of U-bends from left to right, where two U-bends could actually equal four rows. The number of circuits will also affect pricing, and this can be determined simply by counting the amount of returns or distributors you see.

When you have access to all the above measurements, you're all set to get an accurate cost without worrying about factors that could increase your cost and impact profits. There are times when improvisation is needed, and this is when it's 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 to determine the number of rows, a combination of the casing depth and condensing unit capacity can be used to determine this. So, I can 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 what CFM the air handler is running, even better (or I can estimate around 350-400 CFM per ton). I would essentially 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 would ideally bring back a capacity close to the 30 tons we’re calling for, then quoting and consulting with the customer can begin.

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