What is an Evaporator Coil – Differences Between “A” and “Z” Types

This brief guide answers those basic FAQs –

What is an Evaporator Coil & What Does the Evaporator Coil Do?

There are several heat pump and AC evaporator coil types, but they all do the same thing with the same basic parts.

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• Radiator style fins maximize surface area for gathering heat (AC mode) and dispersing heat (heat pump heating mode)
• Copper or aluminum tubing welded to the back of the coil fin assembly that carries refrigerant between the indoor coil and the outdoor coil
• Refrigerant circulated by the compressor in the outdoor condensing unit that absorbs indoor heat (AC mode) to disperse outside or absorbs outdoor heat (heat pump heating mode) to carry indoors to release
• Slanted or Vertical design to condense moisture out of indoor air (AC mode) onto the cold coil, so that it runs into the drain pan and is drained away, lowering indoor humidity
• Size: Evaporator coils come in sizes from about 1 ton of cooling/heating capacity to 5 tons of capacity for residential use. The size of the evaporator coil must be matched to the size of the condensing unit outdoors.

Coil Shapes

A-coils are the most common – the industry standard and used by all brands; Z-coils or N-coils are used by several brands including Carrier and Bryant, Rheem and Ruud; and Slab coils are used in compact AC designs and a few others.

Let’s look at them in this order.

A-Coils

Several manufacturers make A coils including third-party brands. They are used by most of the best AC brands including Carrier, Trane, York, Heil, Goodman and most other brands like Lennox.

Shape: As is obvious from the picture, an A-shaped evaporator coil is built with two slanted sides joined at the top. The refrigerant tubes are attached to the interior of the A shape. You can see the looped refrigerant tubes exiting the coil and looping back in. The tubes run back and forth.

Performance: As the coil and refrigerant collect heat in AC mode, the coil fins get very cold. Moisture naturally condenses on the coil, and the A-shape allows the moisture to flow down and drip into a pan. The pan has a hole in it, and the water runs into it and down a tube to a floor drain or a drain that leads out of the house.

Air from your home’s ductwork flows into the interior of the coil – and out through the outer sides.

If you zoom in on the picture, you might be able to see the razor-thin fins that create a huge amount of surface space. This space allows for the quick, efficient gathering of heat (AC Mode) or dispersal of heat (Heat Mode).

The picture shows screws at the lower right and lower left on the side panel made from sheet metal. There’s a screw at the top, which isn’t shown. To clean the evaporator coil, those screws are removed and the panel taken off. This gives you access to the dirtiest part of an evaporator A coil.

A Coil Evaporator Coil Pros and Cons

Pros: A coils are reliable, easy to clean and are readily available. Many are universal, meaning they are made by third-party manufacturers and work with nearly any brand.

You won’t have to wait days to a week or more for your HVAC technician to find a replacement evaporator A-coil – with the possible exception of Lennox. Lennox makes its own coils, and parts delays are more common.

Cons: There are no inherent negatives. However, as with any other part type, some evaporator A coils are built with better parts and quality than others. If you need your evaporator coil replaced, encourage your AC repair technician to use a brand with a track record of dependable performance.

N- or Z-Coils

Whether the coil is called an N-coil or Z-coil depends on which way it is installed, i.e., whether the furnace is horizontal or vertical (upflow/downflow). There are no performance or design differences between the two.

Due to their shape, some technicians call them zig-zag evaporator coils.

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While not as common as A coils, N coils are used by most brands. Here are a couple examples.

Rheem and Ruud are sister brands made by Paloma Industries. That is, they are identical, which you can see if you review a list of Rheem ACs and the corresponding list of Ruud ACs.

Carrier also uses a range of N coils, as does Carrier’s sister brand Bryant.

Performance is essentially the same with one difference – the N or Z coil has a third leg of radiator-type fins.

N Coil Evaporator Coil Pros and Cons

Pros: Many HVAC technicians believe that Z or N coils are more efficient since they have a third leg of fins. The more fins, the greater the surface area and the greater the ability to collect (AC mode) and disperse (Heat mode) heat. Some N coils are also a bit more compact – though this seems counterintuitive given their design. But it is true.

Cons: There are two significant problems. First, N coils are quite a bit harder to clean. The coil might not get as thoroughly cleaned. Dirt remaining on the coil surface will reduce the efficiency of the coil and, as a result, the AC system. Of less important, it might take longer to properly clean, and an HVAC technician will likely charge $25-$50 more to clean a Z coil evaporator coil.

But there is another concern: Due to the legs being closer to one another in the compact design, N coils are more prone to freeze-ups. We’ve said that evaporator coils get very cold during an AC cycle. Their surface temperature can dip below 32F. When moisture condenses, if freezes, and soon the coil is a “block of ice,” as some techs call it. See our guide called Air Conditioner Freezing Up? Common Causes and How to Fix It to learn more about this potential issue.

Slab Coils

These are the least-used coils, but they do have their place. Performance is essentially the same. The refrigerant tubes are inside the two “slabs” or radiator fin assemblies. Slab coils are almost always used in air handlers and furnaces with horizontal airflow.

Slab Evaporator Coil Pros and Cons

Pros: Slab coils feature compact design ideal for use where space is limited. They are also easy to clean.

Cons: The slabs don’t have quite as much surface space, so efficiency is slightly less.

Goodman AlumaFin7 Coils

Goodman is now a Daikin brand. Daikin, a global leader in air conditioning, has pumped quite a lot of R&D money into Goodman resulting in improved quality and a focus on innovation.

Amana is a brand beneath the Goodman brand, so Amana uses the new AlumaFin7 coil too.

The AlumaFin7 evaporator coil is an A coil.

According to industry news source ACHR News, “Research and development on the AlumaFin7 began two years ago, in response to dealer feedback, demand for a corrosion-resistant product, and company innovations to improve the heat transfer process. The patented technology integrated into the design of AlumaFin7 evaporator coil not only improved the heat transfer process, but allowed Goodman and Amana brand engineers to shorten the height and width of the coil, reducing most matchups by up to 4 inches. Dealers now have a lighter, compact coil that’s only 21 inches deep.”

What Makes the AlumaFin7 Evaporator Coil Different?

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There are several features that distinguish this evaporator coil.

7mm vs the standard 9.5mm (3/8”) refrigerant lines. This picture shows the relative size difference.

Goodman suggests that since there are more lines relative to the amount of refrigerant, it creates greater efficiency. The lines plus the fins are aluminum to enhance resistance to corrosion.

Compact Design: This shot shows the space saving available with the AlumaFin7 evaporator coil.

It’s compact size is, according to Goodman, “an efficient option for installations in space-constrained homes.”

Louvered fins produce more surface area for heat transfer. They are etched with acid to create a surface that sheds water more effectively than non-etched surfaces. Faster drainage means less impediment to airflow and improved efficiency.

The heat-resistant plastic drain pan is shaped so that it doesn’t retain water. All the water flows into the drain. This design should reduce the buildup of sludge and mold in the drain pan.

Why are we giving space to this innovative Goodman evaporator coil? Because Goodman is one of the best-selling AC and heat pump brands. It’s likely that the next time you get estimates for an air conditioner or heat pump, you’ll be offered a Goodman among the other options.

Secondly, when we’re informed consumers, we make decisions that prove best in the long-run.

Here is Goodman’s promotional video for this innovative new design. We’re seeking to inform, not to persuade. We have no connection to Goodman or any other brand.

Finally, it is worth noting that the Goodman/Amana AlumaFin7 evaporator coil won a prestigious 2019 Dealer Design Award for Residential HVAC.

Cased and Uncased Coil

There’s one more issue. Coils come in cased and uncased versions. This image shows both options.

Cased coils have their own cabinet, and they are used in most common air handler and furnace installations. The cabinet is mounted above or below the air handler, depending on the direction of airflow.

Uncased coils generally are mounted inside the cabinet of an air handler of furnace. In customized HVAC installations, the installer might build a cabinet for the uncased coil using sheet metal. This is the case when the installer faces space or design configurations and must innovate the system.

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