There’s a laundry list of what to do when it comes to maintaining an HVAC system, but regular coil cleaning is an item that makes its appearance closer to the top of that list than the bottom. Be they indoor or outdoor, coils need attention, and regularly cleaning them can yield efficiency improvements for customers and increased revenue for contractors. To do this, contractors must understand the fundamental benefits of regular coil cleaning, be able to explain those benefits to their customers, and develop a process for their service technicians to follow.



Coils need to be cleaned because they get dirty. That is the short story. Odor, damage, rust, corrosion, and biofilm are just some of the more complex reasons to clean coils.

“Dirty coils affect the heat transfer capacity of the coil,” said Jonathan Sada, director of engineering and research and development for DiversiTech. “Condenser coils can’t reject heat as effectively, and evaporator coils can’t pull heat out of the air effectively and will cause freeze-ups.”

This visual inspection shows the dirt before coil cleaning and the clear surface after cleaning. - The ACHR News

BEFORE AND AFTER CLEANING: Aluminum microchannel coils accumulate dust primarily on the coil’s face, while traditional fin-and-tube coils accumulate more dirt inside the fin pack. This visual inspection shows the dirt before cleaning and the clear surface after cleaning.

According to Sada, aluminum microchannel coils accumulate dust primarily on the coil’s face, while traditional fin-and-tube coils accumulate more dirt inside the fin pack.

“A clean coil gives the coil the heat transfer capacity as designed by the manufacturer,” said Sada. “A more efficient system isn’t strained as hard, so it will last longer. The increased thermal efficiency also results in a lower energy bill.”



When talking to customers about internal HVAC components, the lack of a visual can make coil cleaning a tough sell, but all it really takes is a little education. When in the home, contractors can point to sources of dirt and debris that coat coils, like dander, pet hair, human hair, and grease, according to Glen Steinkoenig, product manager for Parker Hannifin.

“This solid debris chokes airflow, causing inefficiency, reduced capacity, lack of cooling comfort to the users in the space, and increased cooling costs,” he said. “Also, the moist environment of an indoor coil with this debris can create a place for germs to breed that can cause allergic reactions or even worse [symptoms].”

With these facts, contractors can not only address the well-being of a rarely seen HVAC system, but they can also bring IAQ, comfort, and allergies into the conversation. These tangible elements are things that consumers seem to increasingly care about and are willing to spend money on in order to improve their environment.

Steinkoenig said that outdoor coils get clogged with leaves, dust, pollen, and seeds, and that corrosion can form as well.

“All of this means the cost to operate the air conditioner or refrigeration system is increased,” he said. “The minor expense to clean a dirty coil is insurance against increased energy costs, increased equipment runtime, and increased wear on the system. Besides saving money, this also is an investment in protecting against premature failure of the system or its components.”



Once a customer has given the go-ahead, it’s time for the service technician to get cleaning. Although coils have similarities, each one has its own guidelines, so contractors should consult the manufacturer for specific coil cleaner specifications and unique instructions to ensure they are employing the proper method.

“There are specific cleaners for indoor as well as outdoor coils,” said Doug Gildehaus, director of product development, Nu-Calgon. “Milder chemicals provide versatility to be used for [various] applications when diluted appropriately.”

Cleaning a coil with water, nitrogen, or compressed air is like washing a car with water alone, he said. Detergents in applicable cleaners are required to emulsify grime off the metal surfaces to optimally clean the coil and to ensure that full capability is reinstated.

With the proper cleaner applied to the coil, the technician’s next step is to remove the cleaner, dirt, and debris.

“Rinsing the surface with the water flowing in the opposite direction of airflow will help push the solid materials off the inlet face, where most of it collects,” said Steinkoenig. “For heavily corroded outdoor coils, it is desirable to reduce the corrosion layer that impedes heat transfer and, for this, an acidic-type coil cleaner is best.”

Once the coil is properly cleaned and rinsed, there are after-treatments that can be applied to maintain the cleanliness and further protect against corrosion, dirt, and bacteria.

According to Steinkoenig, the use of a bacteriostat — an agent that inhibits the growth of but doesn’t kill bacteria — can address any lingering bacteria as well as reduce odors.

“It is possible to coat coils with heat conductive coatings to reduce future corrosion and reduce fine particles from sticking to the coil surface,” said Steinkoenig. “It also makes future coil cleaning more effective by ensuring a smooth coil surface that does not hold onto debris well.”



When it comes to how often a coil needs to be cleaned, Gildehaus said it depends on its applications.

“Ideally, the coil should be cleaned annually with the appropriate cleaner — selection is based on install location, coil design, what debris is on the coil, and other application factors,” he said. “Depending on the situation, coil cleaning may need to occur more frequently in adverse environments.”

Sada agrees that annual cleanings will maintain optimal performance.

Although once a year is a good standard measure, Steinkoenig reminds contractors and technicians that coil inspections can and should be performed prior to the start of the cooling season for an air conditioner or every six months for a heat pump.

“If the inspection finds reduced airflow or visual blockage of the heat transfer surface, then a coil cleaning should be completed,” he said. “A thorough inspection involves reviewing not just the outsides, but also the inside and between the coil layers, which often get clogged.”

He suggests that technicians adjust to more frequent reviews in establishments such as restaurants, where airborne grease levels are usually higher.

Publication date: 6/10/2019

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