Replacing Carrier Chilled Water Coils

For HVAC professionals, replacing Carrier chilled water coils is a task that demands precision. One miscalculation in dimensions, connection types, or circuit configurations can turn a straightforward replacement into a significant challenge, leading to delays and complications like compromised airflow or customer callbacks.

Why Precision Is Critical

Carrier chilled water coils are engineered with extremely precise specifications. Even the slightest deviation can result in issues such as:

  • Airflow Restrictions: A poor fit can obstruct air movement, affecting system efficiency.
  • Inefficient Heat Transfer: Suboptimal coils may lead to inadequate cooling performance and increased energy costs.
  • Connection Misalignment: Mismatched connections complicate the installation process and can lead to leaks or failures.
  • Extended Installation Times: Inaccuracies often necessitate additional rework, wasting valuable time on the job site.

It’s crucial to explain the importance of attention to detail to your clients. A so-called “replacement” coil that doesn’t meet specifications can inadvertently introduce new problems rather than solving the existing ones.

The Capital Coil Advantage

In the world of HVAC, many coil manufacturers overlook the significance of these specifications, opting for oversimplified solutions that can create headaches later on.

Here’s where Capital Coil steps in. Whether you have:chilled water coil

  • A clear model tag
  • A partial number
  • Or even just a worn-out coil

We have the expertise to provide a reliable solution. Our team has extensive experience manufacturing the coil types you depend on daily, ensuring you receive high-quality products.

Cross-Referencing Capabilities

In many cases, we can cross-reference Carrier coil models accurately, thanks to our comprehensive manufacturing history. If direct cross-referencing isn’t feasible, we can also work from the drawings you provide, creating a custom solution that meets your precise requirements.

Take-aways 

Replacing a Carrier chilled water coil doesn’t have to be a gamble. By collaborating with Capital Coil, you gain a reliable partner who understands the critical elements of the job: ensuring a perfect fit, optimizing performance, and getting the installation right the first time. 

For additional information or to discuss your specific coil replacement needs, feel free to reach out to the Capital Coil team. Let us help you streamline your projects and enhance your HVAC services!

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Guidelines For Air Velocities

The height, length and resulting air velocities greatly figure in everything in determining the size and performance of a coil. Step # 1 in determining the size and performance of a coil is dependent upon understanding face & air velocities of air across the coil. Whether you use CCA’s coil selection program to help size the coil, or you are replacing an existing coil; the height, length and resulting velocity determine everything.

Hot Water Booster Coils

air velocities

Every coil has a specific, optimum velocity, so you want to make sure you are within 30% (+ or -) of that number. For example, booster coils have an optimum velocity of 800 ft/minute. That means that you can drop your velocity to 600 ft/minute, or conversely, increase the velocity to 1,000 ft/minute. The duct velocities are almost always higher, which means that you will need to transition to a larger coil. Try to get to as close to 800 ft/minute as possible, while sizing your coil to make the transition as easy as possible. Everything with coils is a balancing act.

Hot Water & Steam Coils

Like booster coils, hot water and steam coils should also have face velocities at approximately 800 ft./minute. Both steam & hot water coils have only sensible heating, which is why their face velocities can be the same. Face velocities ultimately control the coil’s cost, so 800 ft./minute really is a heating coil’s “sweet spot”.

If you are purchasing an air handler unit, oftentimes the heating coil is smaller than the cooling coil because the face velocities on heating coils can exceed those of cooling coils. Due to water carry-over, cooling coils cannot exceed 550 ft/minute, while heating coils only deal with sensible heat.

Chilled Water & DX Coils

Due to the limited face velocities of cooling coils, your choices are more limited. With cooling coils, your face velocity must be somewhere between 500 ft./minute-550 ft./minute. Remember that when dealing with cooling coils, you are dealing with both sensible and latent cooling, so the coil is wet. When you exceed 550 ft./minute, water carry-over occurs past the drain pans.

If you are purchasing an air handler unit, you probably will not have worry about the coil’s face velocity as most coils come pre-sized at the acceptable face velocities. Fan coils also come pre-sized with the correct CFM’s. However, if you are replacing an existing cooling coil, the face velocity must remain at or below 550 ft/minute!!

 Air Stratification Across The Coil

Air does not travel equally across the face of a coil. If you were to divide a coil into (9) equal sections, like a tic-tac-toe board, you would see a high percentage of air travelling through the center square, rather than the corner squares. In a perfect air flow scheme, 11% of the air would travel through each of the 9 squares, but that is not what happens. Because more air travels through the center of the coil, you want to avoid putting a fan too near the coil. Due to central air flows, most systems are draw-thru, rather than blow-thru. This is also why you want to avoid installing your coil near any 90 degree angles/turns in the ductwork. Avoid any situations that contribute more than the “natural” air stratification to help ensure your coil is at maximum efficiency.

In some situations involving cooling coils, you will have water carry-over even when the coil is sized correctly. How can this happen? Think about the tic-tac-toe board again. Air velocities are exceeding 700 ft./minute in the coil’s center, while the corners are around 300 ft./minute. This cannot and will not work.

Coils do not have any moving parts. They simply react to the air across the outside of the coil and whatever is running through the inside of the coil. Coils are 100% a function of your entire system, as well as the installation in general.

Capital Coil & Air is here to help with any coil selections that will help avoid costly missteps that lead to wasted time and money. Call us on your next project, we greatly look forward to working with you!

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Why Cooling Coils Need to Be Replaced

In theory, properly engineered and maintained cooling coils should deliver 20+ years of service life. In practice, most coils are replaced prematurely. The root causes are typically operational neglect, environmental exposure, improper application, or design limitations. Below are the three primary drivers of early replacement, along with technical context.

1. Increased Air Resistance from Coil Plugging

Cooling Coils

Failure Mechanism:

Airborne contaminants (dust, pollen, fibers, grease aerosols) penetrate beyond the fin surface and embed deep within the coil core. Once lodged between fins and tubes, they cannot be fully removed by routine air-side cleaning.

Primary Causes:

  • Poor filtration

  • Irregular filter replacement

  • Lack of annual coil cleaning

  • High-particulate environments

Performance Impact:

  • Increased air-side static pressure

  • Reduced airflow (CFM)

  • Decreased heat transfer 

  • Reduced system capacity and efficiency

Plugged cooling coils often force the fan to operate outside design conditions, increasing energy consumption while lowering cooling output.

2. Freeze Damage

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Failure Mechanism:

Water trapped in coil tubes expands during freezing, generating internal pressures sufficient to rupture copper tubes.

Why It Happens (Even When Dormant in Winter):

  • Circuiting designs that prevent full drainage

  • Drain connections positioned above low tubes

  • Lack of glycol protection

    broken return bends

  • Inadequate winterization procedures

Consequences:

  • Multiple hidden leaks

  • Thinned tube walls due to pressure expansion

  • Progressive failures after initial repair

  • High risk of recurring leaks

Once a coil experiences extensive freeze damage, repair becomes unreliable. The metallurgical integrity of the tubes is compromised, making replacement the only durable solution.

3. Corrosion

https://static.wixstatic.com/media/ea3647_d85a052e6f8a4b5ab1c1d0555c623a28~mv2.jpg/v1/fill/w_1000%2Ch_750%2Cal_c%2Cq_85%2Cusm_0.66_1.00_0.01/ea3647_d85a052e6f8a4b5ab1c1d0555c623a28~mv2.jpg
Corrosion occurs on both the air side and the fluid side, often simultaneously.

Air-Side Corrosion

  • Salt-laden atmospheres (coastal or industrial)

  • Hydrogen sulfides (e.g., wastewater treatment facilities)

  • Chemical exposure in manufacturing environments

Visual Indicator:

A white ring around the tube-to-fin interface. This indicates loss of mechanical bond and reduced thermal conductivity between tube and fin.

Effects:

  • Reduced heat transfer

  • Loss of tube/fin contact

  • Core blockage from corrosion byproducts

  • Elevated air pressure drop

Water/Refrigerant-Side Corrosion

  • Raw, untreated water

  • High mineral content

  • Improper water chemistry control

Internal corrosion weakens tube walls and leads to pinhole leaks, particularly in copper tubing exposed to aggressive water conditions.

 

Key Takeaway

Cooling coil replacement is common—but preventable. Most failures are not random; they are the result of design limitations, environmental exposure, or maintenance gaps. Replacing a coil without diagnosing the root cause often guarantees another premature failure.

If longevity, efficiency, and reliability matter, the solution isn’t just replacement—it’s engineered improvement.

 

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Looking For A Trane Replacement Coil

If you need Trane replacement coil within a Trane system, but aren’t sure about the dimensions or decoding the model #, send this to Capital Coil & Air for pricing. On most Trane AHU’s, the AHU model #, as well as the coil or “part #”, is listed as “Service Model No Coil”. If you see this, send it over, and the sales team at Capital Coil will handle the rest. Great pricing with the ability to be built as fast as is needed!Trane replacement coil

Top 5 Reasons Commercial HVAC Coils Prematurely Fail

Capital Coil & Air has come across virtually every scenario over the years in which a commercial HVAC coil had to be prematurely replaced, and we have since created an easy guide targeting the main reasons HVAC Coils prematurely fail.

  • Coil Plugging: If you are not changing filters and/or your commercial HVAC coils are not properly cleaned in a timely manner, your coil will actually begin to act as a filter. When dirt builds up on the coil, that blockage prevents heat transfer and can cause an approximate 20% to 40% drop in performance. Dirt adds to the coil resistance and can be a primary cause for your coil to fail prematurely.
  • Vibration: When your HVAC coils are installed near a moving piece of equipment, vibration can occur and cause leaks. You can tell if vibration is the main cause if leaks are near the tube sheet and look like they are slicing through the tube. If/when that happens, the coils should be isolated from the rest of the system to prevent vibration from causing damage. One way to combat this is by oversizing the tubesheet holes, but many manufacturers will not do this. Condenser Coils are usually the most common victims of vibration.
  • Corrosive Environment: This applies to both the air in the environment and inside the tubes. For instance, if there is a corrosive element in the air, it will eat away at the copper tubes; whether you have 0.020” wall or 0.049” wall. This is very common in coastal areas where there may be salt in the air. To keep the costs down from going to a stainless steel or cupro-nickel coil, we usually suggest coating the HVAC coils. Coatings are almost always within your budget, and its application will only add about a week to the overall lead time. Steam condensate and untreated water can cause corrosion within the tubes of HVAC coils as well. If you have a steam coil that has failed before the one year warranty, there’s a great chance that corrosive agents are in the steam, and it’s eating away at the copper tubes.
  • Freeze-Ups: Most people think that when HVAC coils freeze, the water or condensate laying in the coil freezes into ice and it expands causing the tubes to bulge and eventually spring leaks. What really happens is that the coil will freeze in multiple areas simultaneously, and it’s the pressure between these areas that cause the tubes to swell and eventually burst. These are very easy to spot as the leaks will run the length of the tube rather than around the tube.  ALSO be very careful when considering “freeze-proof” coils!  If you remove 5-6 inches from the fin length to make the “freeze-proof” application fit, your coil’s performance will suffer considerably. 
  • System Design: You would be amazed to learn how many HVAC coils were never designed properly for their systems. If there is a design problem, replacing the coil will only waste time and money; while you have done nothing other than duplicate the previous problem. A little known fact in the replacement market is that a high percentage of all our projects are because the coils were built incorrectly or were never designed correctly in the first place. In some cases, owners attempt to improve the coil’s performance by adding additional rows. Most however do this without taking into account the air pressure drop or fluid pressure drop that comes with it.

When dealing with an HVAC coil manufacturer, try to partner up with one who will walk you through the engineering and explain it along the way. Capital Coil & Air has well over a decade of experience and can help you diagnose whatever problem that you are experiencing correctly the first time. We look forward to working with you on your next project!

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Different Types of Steam Coils

There are two types of steam coils:  standard steam coils, which are used in most reheat applications, and steam distributing coils, which are used in applications where the entering air temperature is below 40 F degrees.  Many times, this type of coil is also known as a “non-freeze” coil, but that name is misleading because in reality, there is no such thing as “non-freeze”. 

Standard Steam

Standard steam coils operate a lot like hot water coils, but the construction is very different even if the coils appear to be constructed the same.  The supply and return connections are often on the same end like a hot water coil.  But, steam is very different than hot water, and the coil must be built for and circuited for steam.  Keep in mind that steam is always more erosive than hot water.  The brazing and tube wall thickness must account for steam. ALWAYS remember that even low pressure steam is more erosive than hot water, and a steam coil needs to be built accordingly.

Steam Distributing (Non-Freeze)

Steam distributing coils are a completely different type of coil because they are constructed as a tube within a tube. Every place that you see an outside tube or header, there is an inside tube and header that you can’t see. The steam on the inner tube keeps the condensate in the outer tube from freezing.  The purpose of the Steam Coiloriginal coil design was to distribute the steam evenly along the length of the coil and to eliminate any dead spots on the coil.  A byproduct of this coil was also found.  The coils didn’t freeze nearly as easily as the standard steam coil, so the coils became known as “non-freeze”, which as mentioned, is not completely accurate.  Any coil can freeze under the right conditions, but, this design is what needs to be used when the entering air is under 40F degrees!!! 

Steam Coil Design

Steam coil designs can be very tricky.  Steam coils are totally a function of the system and installation, while other coils operate more independently of the system.  There needs to be correctly designed traps, and they need to be installed in the correct place and depth in the system.  Often, vacuum breakers are also needed in the system.  The piping must also be installed correctly to make sure the steam is entering the coil and not the condensate.  Even with all of those factors, you’ll need a correctly designed steam coil that matches the steam pressure, length of the coil, and the entering air temperature.  Coils can freeze easily.  Coils can be too long in length and the steam cannot travel the length of the coil and distribute evenly.  Condensate can easily be trapped somewhere in the coil, and the result is water hammer. 

Capital Coil & Air has years of experience designing steam coils, and is here to answer any questions and help to design the right coil for your project! 

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Chilled Water Coils – Circuiting Made Easy

Chilled Water Coil

Circuiting chilled water coils is one of life’s great challenges in the coil business. You’re bound to run across folks with years of experience in the industry that can not effectively explain this concept. While not the most exciting of subjects, the necessity of circuiting chilled water coils can not be overstated. Capital Coil & Air has attempted to simplify the idea of circuiting as much as possible.

For starters, circuiting chilled water coils is ultimately up to the performance of those coils. Circuiting is really a balancing act of tube velocity and pressure drop. In other words, think of a coil as a matrix. Each coil has a specific number of rows, and a specific number of tubes within each row. For example, a chilled water coil might be 36 inch fin height and 8 rows deep. The coil has 24 tubes in each row, and multiplied by 8 rows, there is a total of 192 tubes within the coil. While you can try to feed any number of tubes, there are only a few combinations that will work.

    • Feeding 1 tube – you will be making 192 passes through the coil, which will essentially require a pump the size of your car to make that process work.
    • Feeding 2 tubes – equates to 96 passes, and your pressure drop will still be enormous.
    • Feeding 3 tubes – 64 passes, which is still too many.
    • Feeding 4 tubes – See above.
    • Feeding 5 tubes – Impossible as 5 does not divide evenly into 192 (passes).
    • Feeding 6 tubes – Still constitutes far too many passes, which again leads to additional pressure drop.
    • Feeding 7 tubes – Same rule for feeding 5 tubes.
    • Feeding 8 tubes –  Same rule for feeding 6 tubes.
    • Feeding 24 tubes – This feed consists of 8 passes, which is in the ballpark, and with a pressure drop you can live with.
    • Feeding 32 tubes – 32 tubes will see 6 passes. You might see a slight decrease in performance, but it’s off-set by a continuously better pressure drop.
    • Feeding 48 tubes – The magic combination, as 4 passes typically elicits the best performance and pressure drop simultaneously.

 

Rule #1: The number of tubes that you feed must divide evenly into the number of tubes in the chilled water coil.

Rule #2: The chilled water coil must give you an even number of passes so that the connections end up on the same end.

Rule #3: Based on the number of passes, you must be able to live with the resulting pressure drop. Acceptable tube velocity with water is between 2 and 6 ft. per second.

You’re bound to run into different terminologies depending on the manufacturer. More times than not, the different verbiage confuses more than it clarifies. However, understanding the basic tenets of chilled water coil circuiting will remove much of the perceived difficulty.  

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Top 10 Fan Coil FAQ’s

1. A fan coil is among the easiest units to understand in the HVAC industry.  Basically, there is a small forward curved fan, a coil, and sometimes a filter.  They are all direct drive units. Click HERE to see Capital Coil’s full Fan Coil Product Lineup.

2.  Fan coils run from 200 CFM to 2200 CFM, which is 0.5 ton through 5.5 tons.  Anything larger than these sizes requires a belt drive unit…which is really a full fledged air handler.

3.  The thing that differentiates fan coil units is where and how they are going to be installed.  Is the unit going to be hidden above the ceiling or maybe in a closet?  Or is it going to be exposed so that everyone can see it?  Will it be ducted or will it just pull air from the space where it’s located?  These are things that determine the configuration of the unit and which style of unit to choose.  But, every unit has 3 things in common:  fan, coil, and sometimes a filter.

Fan Coil 4.  Some units have (2) coils.  One for heating and one for cooling.  Obviously, there is a separate supply and return connection for each coil and these units are known as 4 pipe fan coils.  Many units only use the same coil for both heating and cooling and these units are 2 pipe fan coils.

5.  Units are either horizontal or vertical depending on the orientation and flow of the air.  A typical fan coil in a hotel room is a vertical unit with a mixture of air coming from outside and the air recirculating in the room.  The air enters at the bottom of the unit and is drawn upward through the fan.  This makes the unit a vertical style.  Many units are horizontal with the air entering at the back of the unit and traveling horizontally through the unit.

6.  Almost all fan coils are 3 speed or infinite speed settings based on the controls.  The high speed gives you more BTU’s, but more noise too.  Because the unit is direct drive, when you dial down the speed, you also dial down the performance.

7.  Coils in the units tend to be 3 or 4 row deep coils.  3 row is typically used the most, but if you need the extra performance, 4 row is the way to go.  Performance is always governed by the cooling aspect.

8.  Fan coils sometimes have short runs of duct work and there is static pressure on the unit.  Static pressure reduces the amount of CFM and BTU’s that the fan coil can give you.  This is true of both horizontal and vertical units.  Most performances listed on charts that you will see are static free performances.

9.  The control systems for fan coils are often more complicated and more expensive than the units themselves.  There are balancing valves, isolation valves, unions, y-strainers, p/t plugs, air vents, ball valves, thermostats, condensate float switches, and disconnects.  Capital Coil & Air can do this at the plant, but it is much cheaper and easier to do it at the installation. 

10.  Just describe your installation requirements to a sales engineer at Capital Coil & Air and they will guide you to the right design and configuration of the unit for you.  It requires only a phone call or e-mail! We look forward to working with you!

 

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What Is Meant By A “Bank” Of Chilled Water Coils

For those that work with HVAC installations on a regular basis, you have run across the problem of needing to install new chilled water coils in very tight, confined areas. The coil is too big to fit in the Chilled Water Coilselevator, and/or the HVAC room is so small that you are likely to damage the coil simply by moving it. As a solution to this challenge, chilled water coils are often installed in “banks” of coils. You are most likely to see this configuration in Air Handler Units, as well as “built-up” systems. Due to face velocity limitations across the coil, you will need larger coils in order to meet your required face area. With this in mind, there are a few specific reasons why you want to avoid having a single, large coil in one of your units.  Starting with the obvious: larger coils are much more difficult to transfer and install. This is especially true for older buildings, where the rooms were essentially built around the HVAC system.

As you’ve probably experienced, some of these areas can barely fit a single person, so installation – if even possible – is a logistical nightmare. Also, the larger the coil, the easier it is to damage during transport to the jobsite. To avoid these issues, simply break down the single, larger coil into smaller coils. When piped together, those smaller coils are stacked into “banks” of coils in the system. If installed correctly, this “bank” should have the same performance as the larger, single coil.

Casing

There are many different casing options available, but “stackable” flanges are required for heavy chilled water coils that are “banked”. The flanges are often inverted inward and down to give added strength to the casing, which is needed due to the fact that another coil of equal weight will be stacked on top of it. When ordering coils in a “bank” configuration, be sure to let the manufacturer know that they will be “stacked”.

Many engineers also use stainless steel casings on chilled water coils. While more expensive than traditional galvanized steel, stainless steel protects against excessively wet coils and/or corrosive elements in the airstream. Keep in mind that the majority of coils fail because of old age and its casing, as opposed to failure with the coil’s core. With that in mind, doesn’t it make sense to select heavy-duty stainless steel casings that are more durable and meant for stackable installations?

Drain Pans & Water Carryover

Water Coils

All chilled water coils must be sized so that the face velocity across the coil does not exceed 550 ft/minute. Water on the outside of the coil is carried away from the coil’s leaving air side in an arc, while water in the highest point of the coil is carried further down the unit or ductwork. “Stackable” coils often require intermediate drain pans under each coil to catch the excess water carryover. Each coil in a bank requires its own drain pan, as a single, large pan under the bottom coil is not enough.

Circuiting/GPM

If all of the coils in a “bank” are of equal size and handling the same CFM, then the GPM of each coil will also be the same.

Always feed the bottom connection on the supply header on the leaving air side of the coil. This ensures counter air and water flow. This also prevents the coil from short circuiting because the header fills first and circuits all of the tubes equally.

Designing Banks Of Coils

Almost all coil “banks” perform more efficiently if you design something more square in shape, as opposed to long and/or high. In a “bank” of coils, you may find that one coil has points of 300 ft/minute, with other points at 800 ft/minute. Scenarios such as this will cause water-carryover! You generally want to be as close to 550 ft/minute as possible in order to allow equal airflow distribution across the face area of the coil.

Anytime you are designing and/or building coils, work closely with the manufacturer as an added resource to ensure that you are getting the ideal solution for your HVAC system. Capital Coil & Air works on similar jobs such as these daily, and we welcome the opportunity to work with you in whatever capacity is needed.

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Top 10 Tips For Measuring HVAC Coils

1. When measuring HVAC coils, performance has very little to do with accurately measuring for replacement coils. Fitting the coil in the existing space with the least amount of labor has everything to do with measuring a coil.  If you duplicate the coil in almost every respect, the performance will match and take care of itself.  New is always more efficient than old.

2.  If you’re ever in doubt about a dimension, smaller is always better than bigger. You can always “safe off” around any coil as long as you can fit it in the space.  If a coil is too big, it makes a really ugly coffee table in your shop.  Too big is the enemy of measuring coils.

Chilled Water Coil

3.  The fin height and fin length are not the determining factors in measuring a coil. The overall casing dimensions are the most important, and you work backwards to determine fin dimensions.

4.  The depth of any coil is the total casing depth in the direction of airflow. The height is the number of tubes high in any row.  Depth is a function of rows deep and height is a function of tubes in a row.

5.  Overall length (OAL) is not the fin length and it’s not the casing length. It is the length from the return bends to include the headers that are inside the unit.  Again, it is necessary to work backwards to get the other dimensions once you know this critical dimension.

6.  Circuiting is the number of tubes connected to the supply header. Generally, you just want to count the number of tubes connected to the header and that will tell you whether it’s full, half, or even a double circuit.  It does not matter how the return bends are configured.  Your goal is to count the number of supply tubes and all performance is based on that.

7.  Fins are measured in fins per inch. Hold a tape measure up to the coils and count the number of fins in one inch.  If you can’t get in to take the measurement, a safe rule of thumb is 10-12 fins/inch.  That will work on almost every coil.  The exception to that rule is a condenser coil.  14-16 fins/inch on a condenser coil is usually pretty safe.

8.  Connection locations are difficult only if you are using the existing piping in the system (which are welded). Copper piping is brazed and can be changed easily.  If a system is old and the piping is being replaced as well as the coil, the connection location is not a major deal.  It’s very easy to match up!

9.  With replacement coils, the concept of “left hand vs. right hand” doesn’t actually exist. Connections are “top left-bottom right” or vice versa.  Ideally, all coils should be counter-flow which means that the water and air flow in opposite directions.  The air hits row one first and the water is piped into row eight first.  However, there are lots of installations that are piped backwards, and they work just fine.  Just match them up, and the coil’s performance will be equal to the old coil.

10.  Connections are not measured from the top of the header! They are measured from the top of the casing to the centerline of the connection.  Or the bottom of the casing to the centerline.  You need a point of reference, and the header height can be anything just as long as it doesn’t stick above or below the casing height.

 

All of the above “suggestions” or “secrets” are in no particular order.  They are just things that you should know to ensure that you are selecting the correct replacement coil. While most seem like common sense, your best bet is to talk with the sales team at Capital Coil & Air, who can walk your through the entire process and help you to fill out coil drawings when trying to measure the dimensions.

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