All About Coil Cleaning

Posted on 11/29/2022

Coil cleaning is a key preventative maintenance task that helps HVAC systems operate efficiently. We’re here to help you understand the differences between evaporator and condenser coil cleaning, know how to determine when coils need to be cleaned, and understand a few basic safety practices for cleaning wet coils. 

At its most basic function, an HVAC system is responsible for moving conditioned air throughout a given space. However, to operate at its peak, the system must both move clean air and efficiently reach the necessary temperature. Therefore, a system must be maintained so all of its parts function at their best. This is why service technicians often perform preventative maintenance — which basically means fixing things before they break!

An important HVAC preventative service is cleaning the evaporator and condenser coils, which represent bookends in the heat exchange process — meaning their upkeep is paramount to the HVAC process overall.


Evaporator and Condenser Coils

An HVAC system typically consists of both evaporator and condenser coils. The evaporator coils are normally located inside a space attached to the furnace or air handler, while the condenser coils are most often located outside.

Each set of coils has their own function within the system. Simply put, the evaporator coils absorb heat and moisture from inside a space, and cooling coils dehumidify air and cause condensate water to drip off the coils and into a drain pan. Condensate then exits the pan through the drain line.

How Debris Affects the Coils

Evaporator and condenser coils are vulnerable to issues, since they’re not only involved in moving air and removing moisture, but also due to their respective locations. For example, since the evaporator coils are inside the system, they are prone to bacteria, particulate and suspected microbial growth, and other particulate growth that can negatively affect the air quality inside a space, as well as the performance of the HVAC system. As for condensers, since they are outside, they may be susceptible to hail damage and various types of yard debris.

While there are great passive defenses such as air filtration, debris will inevitably get into an HVAC system. “Whatever debris makes it past the filters deposits on the coil sets,” said Robert Rizen, ASCS, CVI, Vice President of GC Industrial. “This can lead to debris coming loose from the coils and traveling downstream into the ductwork.”

When either coil is dirty, the system loses efficiency. For example, a clogged condenser coil expels less heat, which forces the system to work longer or harder. Inefficient performance such as that can wear out other parts of the system, potentially causing larger issues in the future.

On the evaporator side, a dirty coil takes longer to cool a space, restricts the amount of air flow delivered, and inhibits water removal from the air, all of which can create moisture. “Moisture can create excessive humidity,” Rizen said. “And that can lead to strange smells, microbial growth, and even affected building materials.”

Coil cleaning is an effective bit of preventative maintenance for a system, and it’s why Rizen most often recommends coil cleaning whenever he performs duct cleaning. But, since the coils are so important to the function of an HVAC system, there are various steps to take to properly clean them.

The Coil Cleaning Process

The coil cleaning process can most often be broken down into four steps, all of which are recommended by ACR, The NADCA Standard. These include: 

  1. Assessment
  2. Visual inspection
  3. Dry cleaning
  4. Wet cleaning

When a homeowner or facility manager calls Rizen, he first assesses that none of the issues are due to a larger cause. A clean evaporator coil won’t help if the compressor is failing or low on freon.

From there, if all other systems are operating, Rizen visually inspects all sides of the coils. “I am going to try and take the coil compartment apart, or cut an access opening, so I can see if the incoming side of the coil is matted up with debris,” he said.

Once the coil is inspected and determined to be dirty, a technician may dry clean the coil, which involves the physical removal of debris. “Trying to capture the dust and dirt with a negative air machine locally at the coil compartment as you work is highly recommended,” said Rizen. “Other times you use a vacuum with a soft brush at the end of it, or you can use a plastic coil comb to rake as you vacuum.”

After dry cleaning, if upon another visual inspection the coils still appear dirty or have suspected microbial growth, a technician should then move on to wet cleaning, or using a chemical cleaner for the coils. But chemical cleaning can be abrasive and potent, so it’s important for technicians to use them safely.


Best Practices for Wet Coil Cleaning

Simply put, wet cleaning is applying a chemical onto a coil, letting it sit for a certain amount of time, and rinsing it with water. However, evaporator and condenser coils are made from various materials. In commercial spaces, coils may be made of copper and stainless steel, while residential spaces may be coated, microchannel, or copper mixed with aluminum and other metals

Determining which material makes up the coil should be done before attempting to wet clean, as chemicals can cause massive damage if misused. “Read the label,” Rizen said. “Know what product you’re using, what’s in it, proper dilution ratios, and the dangers of skin contact and inhalation.”

Once the right chemical solution is chosen, there are different approaches for wet cleaning both the evaporator and condenser coils. “Water control is key with evaporator coils,” Rizen said. “Residential drain pans, for example, are often only an inch deep, which means they fill up fast, and any overflow pours out the bottom of the system.” Overflowing can mean water in the next room, soaked drywall, or even ruined system electronics, which can create additional problems for a technician.

For condenser coils, though they are outside and may be unimpacted by potential overflow, there are other potential dangers from misuse. “It’s more important with condensers to get the chemicals diluted, flushing them with plenty of water,” Rizen said.

Improperly diluted chemicals can have far-reaching effects on particular spaces. For residential systems, chemicals can seep into soil, kill grass and other vegetation, or remain a hazard for people or pets who may occupy the area. For commercial properties, chemical run-off can damage the roof itself.


Coil Cleaning as a Next Step

While coil cleaning is considered preventative maintenance, the function of the coils means a lot to the overall performance of an HVAC system. Coil cleaning can be a complex service to perform, and requires both care and patience. Before any technician approaches coil cleaning, Rizen recommends reviewing ACR, The NADCA Standard.

When undertaken with proper precautions, cleaning coils is a clear next step to ensuring an HVAC system continues to function at peak performance.

This article originally appeared in the July/August 2022 edition of DucTales.



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