Evaporator Coil Cased Vs Uncased – Which To Choose?

The evaporator coil is one of the essential parts of an HVAC system. This component is responsible for removing the heat from the outside air and lowering the humidity.

And if you're the type to be hands-on with your HVAC system, you may have heard of cased and uncased evaporator coils. That's why we investigated this topic to help you decide which one to choose, and here is what we discovered.

Cased Evaporator Coils:

These coils are horizontally oriented and typically have a metal casing covering them.

They serve a similar function as vertical coils and are one of the most frequently utilized in air conditioning systems, except for size and shape.

Depending on how the air conditioner is set up, a cased or vertical evaporator coil may suit better for installation.

Uncased Evaporator Coils:

Uncased evaporator coils have no exterior covering and can be positioned either vertically or horizontally.

They are suitable for special air conditioners that may need experts to modify the coil form to fit the equipment because they lack coverage and are easily adaptable.

Continue reading as we elaborate on the pros and cons of each evaporator coil type. We'll also tackle how the evaporator coil works, what common evaporator coil issues you might encounter, and how to fix them. With that said, let's dive right in!

A comparison between cased and uncased evaporator coil, Evaporator Coil Cased Vs Uncased - Which To Choose?

How Do Evaporator Coils Work?

Evaporator coils are crucial for your air conditioner to operate correctly and maintain the ideal temperature in your house or place of business.

Evaporator coils chill and condition the air expelled from your air conditioner, much as the electrical coils that makeup heat strips warm the air that exits your heater.


Your air conditioner operates by luring outside air into your house. The heat is dissipated when the air flows over the evaporator coils. The condenser unit and evaporator coils work together to condense the water in the air, lowering the humidity.

In this manner, the air released into your residence or place of business is cold and dry, improving the climate during the sweltering summer months.

What Are The Types Of Cased Evaporator Coils And Their Pros And Cons?

There are three typical subtypes of evaporator coils in this category, namely:

  • A Coils
  • N Coils
  • Slab Coils

A Coils

Air conditioner evaporator being cleaned with a foaming agent

A Coils are most frequently used in vertical air conditioners, where the air travels up or down as it passes through the coils. They are named for the shape they acquire within the case, which resembles a capital "A."

This subtype can hold enough refrigerant to function with respectably high efficiency.


  • A coils are dependable, simple to maintain, and easily accessible. Many are universal, which means they are produced by outside companies and compatible with almost any brand.
  • With the probable exception of Lennox, you won't have to wait more than a few days to a week for your HVAC expert to locate a replacement evaporator A-coil. Lennox produces its coils; thus, there are more frequent parts delays.


  • There aren't any inherent drawbacks. However, certain evaporator A coils are manufactured with superior materials and higher quality than others, just like any other type. Encourage your AC repairman to pick a brand with a reputation for reliable performance if your evaporator coil needs to be replaced.

N Coils

N Coils, like A Coils, derive their name from the configuration of the coils within the casing, which resembles a capital "N." They are suitable for horizontal and vertical air conditioners, where air enters the unit on one side and exits on the other.

It is significant to note that N coils are becoming more and more popular because they are more energy-efficient and smaller than the alternatives.


  • Since N coils feature a third fin leg, many HVAC technicians think they are more efficient. The surface area and ability to collect (in AC mode) and disperse (in Heat mode) heat increase with the number of fins.
  • Some N coils are also a little bit smaller. Even though, given how they are made, this seems counterproductive. But it's accurate.


  • Cleaning N coils is significantly more difficult. The coil might not be cleaned as thoroughly. This will lower the effectiveness of the coil and, consequently, the AC system if dirt is left on the coil surface.
  • N coils are more susceptible to freeze-ups in the compact version since the legs are closer. As we've already mentioned, the coils get very chilly during an AC cycle. The temperature of their surface can fall below 32 °F. A "block of ice," as some technicians refer to the coil, is what happens when moisture condenses and freezes.

Slab Coils

The least popular kind of coils on the market are slab coils. They are typically employed for horizontal air conditioners.


  • The compact shape makes slab coils perfect for use in small spaces. Also, they are simple to clean.


  • Because the slabs don't have as much surface area, efficiency is slightly lower.

What Are Uncased Evaporator Coils?

As mentioned, uncased evaporator coils can be used with horizontal or vertical air conditioners. Since there is no outside shell, they are perfect for systems that need customization.

As a result, it is simple to put the coils' shape in the right location.

It is crucial to remember that after purchasing an uncased evaporator coil, you could require the assistance of a skilled specialist to modify the shape to fit your appliance.

Common Evaporator Coil Issues You Might Encounter And How To Fix Them

We'll now go over typical issues that an evaporator coil could have. These are:

  • Frozen Coils
  • Unit Leaking
  • Dirty Coils

Frozen Coils

Frozen and rusted evaporator coil

As weird as it may seem, if an evaporator coil freezes, it will affect the unit's ability to cool the air that travels through it.

The reason for this, even though it may appear paradoxical, is that the coolant inside the coil is meant to absorb the hot air outside the coil.

A film of ice works as an insulator and prevents the hot air from being absorbed if it is present on the outer tube.

The appliance will still operate in this scenario, but the desired cooling effect won't be present.

How To Fix It:

Find out what is preventing the unit's airflow. The system's balance is upset when appropriate airflow is reduced or restricted.

Start with the most obvious: check for crimped or damaged tubes and ensure that nothing obstructs the airflow into the unit, especially if you are working with a window unit that has just been installed.

Check the refrigerant level to ensure it is adequate, as this is another typical cause of restricted flow.

Unit Leaking

Air condition unit refrigerant fluid leaking with with white fome freon chemical

Usually, leaks happen in the coil. The system will certainly become unbalanced if there is a leak. It will force the AC unit to work harder, putting more strain on it and eventually leading to further issues.

Do not wait to repair your air conditioner if there is a refrigerant leak.

Cooling refrigerant is a dangerous chemical component that should not be inhaled or handled because it can harm the skin and create respiratory issues. It is also harmful to the environment and animals.

In addition to all of that, your AC system will be harmed. Leaks will cause the coils' outside to corrode. Additionally, it will shorten the coil's lifespan by causing wear and tear.

What To Do If Your Unit Is Leaking:

Leaks are fortunately simple to identify. If you find one, it is preferable to consult a specialist rather than attempting to resolve it yourself.

Dirty Coils

Man cleaning air conditioner indoor unit

It is astounding how most units are out there suffering under the weight of dirt and debris, even though this seems like an apparent problem.

Clearly, a dirty coil cannot effectively carry out its functions. Indeed, a small amount of dust won't harm it.

However, excessive dirt can insulate the coil, just like with ice formations, preventing the coil from efficiently absorbing heat.

To Clean Dirty Coils:

Fortunately, fixing it is quite simple and should become part of routine maintenance.

The initial step would be to clear away any collected debris. Debris frequently discovered near the coils includes leaves, grass, and errant plastic bags.

There is no shortage of information on how to clean the unit, but all you need is a hose, a good spray cleaner, and a good brush. After misting the coils, gently brush each coil with a soft brush.

Once the coil has been thoroughly cleaned with a hose, turn the unit back on.

For a deeper knowledge of how to clean dirty evaporator coils, go check out this article: How To Clean Evaporator Coils On Central Air Conditioner.

When Should You Replace An Evaporator Coil?

Although coil leaks caused by refrigerant can be fixed, replacing the coil is the best option.

As every time you have to conduct this repair, you also need to recharge the system with new refrigerant, the long-term cost of this may be cheaper than the cost of repairs.

Only between 50% and 75% of the performance efficiency of the coil will be restored after repair.

If you want to know how much time it takes to replace an evaporator coil, you can check out this post: How Long Does It Take To Replace An Evaporator Coil?

In Closing

In choosing between cased and uncased evaporator coils, it is best to let a qualified technician assess what type of coil you need based on your HVAC situation. 

A qualified contractor can access either a cased or uncased coil if that is what is required for servicing.

Since the same issues mentioned previously can arise, people should never try to access the coil themselves.

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