By Bob Baker

Today, there are a number of coil cleaner choices for the technician. In a way, this is good. This selection holds the promise of being able to select just the right product for the specific cleaning challenge you face on each job. In reality, there are a couple of problems with this abundance of selections. First, making a really informed choice would require knowledge of soil and surface conditions that we may not have available, formulation details that the cleaner manufacturer for competitive reasons may not want to release, and a grasp of chemistry well beyond the scope of most high school chemistry classes. Second, few technicians are willing to carry a wide selection of cleaners to each job. As a result, most try several products and settle on a favorite that they use on most jobs. Some carry a couple of different products that they use for specific applications such as acid for condensers and alkaline for evaporator coils. Is this approach correct? Is there a better approach short of becoming a chemical engineer? Possibly, some understanding of cleaning technology will lead to a more informed choice.

Types of Products Available

What do all the terms mean? The terms acid, alkaline, and neutral refer to positions of a scale of pH ranging from 1 to 14. (Actually, a solution can have a pH below 1 and above 14 but this range is most commonly used) A pH of 7 is neutral and numbers below that are in the acid range and those above that indicate an alkaline solution. We often think of a pH of 7 as being desirable because the fluids of a human body are close to this value. Thus, if we experience contact with a solution either above or below that point, we may find it irritating. Actually, if the pH of a solution that contacts our unprotected skin is significantly above or below a pH of 7, it can severely damage human tissue. Often, we refer to products that are highly acid (below pH 3) as corrosive and those that are highly alkaline (above pH 11) as caustic. Those are pretty scary words (and rightly so) and such products are usually treated as hazardous chemicals requiring special shipping and handling procedures. The labels on such products normally direct the use of gloves, eye protection, and sometimes respirators for safe use.

Why would someone choose to use products with such a high potential for injury? The answer is simple. They work! The types of soils that we encounter in air-conditioning systems can be extremely difficult to remove. Grease and oil-based soils are responsive to high alkalinity. These types of soils are often encountered on evaporator and other internal air-handler surfaces. The oils come from human and animal skin flakes, cooking, and other inside sources. Particulates, smoke, and other environmental soils tend to be responsive to acid solutions. This makes acid type cleaners especially popular in exterior applications. In addition, any solution with a pH at either end of the spectrum reacts with metals. While this reaction creates a significant mechanical (bubbling) action that contributes to the cleaning effectiveness in removing the soil, it also removes with it a small layer of the metal the solution reacts with. These cleaners tend to be relatively inexpensive as the ingredients that impart both high and low pH are cheap and plentiful. So, it is possible to formulate effective cleaners by using less of the other more expensive ingredients.

Along with their desirable properties, very high and low pH cleaners carry with them other concerns. The chemical reactions between these cleaners and the soil and metallic surfaces may produce irritating or toxic fumes. Not only can these harm the technician using them; they can be carried through the air ducts and into conditioned spaces if not used very carefully. Even where the fumes are not sufficiently concentrated to be an actual danger, their odors can lead to occupant confusion that results in evacuation of a facility and corresponding loss of productivity and poor publicity. Some persons have claimed injury in the face of noxious odors even where there is no clinical evidence of harm. Finally, the minor etching of heat exchanger fin surfaces that these chemicals cause can interfere with the orderly flow of condensate water from the surfaces. The microscopic pits that are etched in the surfaces can hold water and cause it to bead up. Those beads of water can then be carried into the ducts by the air stream. Such excessive moisture in a duct will result in growth of bacteria or fungi and an indoor air quality ("IAQ") problem will result.

With the apparent disadvantages of acid and alkaline cleaners, more neutral cleaners would seem to be an ideal solution. This may well be but depends on several factors. First, few neutral cleaners are really neutral. Formulations with pH anywhere from 5 to 11 have been marketed as "neutral". This is because, although not technically neutral, such formulations may not have the strong reactivity that the very acid or alkaline ones do. Unfortunately, a strictly neutral formulation may not have very good cleaning power. Some reactivity is desirable. Finally, there are many variations in neutral (or pH balanced) cleaners. Some use high levels of solvents to cut oily soils. These solvents may give off fumes that are as objectionable as the fumes from corrosive or caustic mixtures and can also be air quality threats.

The best neutral type cleaners are detergent based. That means that one or more detergent surface-active ingredients are formulated together in such a way that they provide a high level of cleaning activity and very low toxicity. Some of these products are also formulated with detergents that are readily biodegradable and thus are not harmful to lakes and rivers into which the rinse water may be carried. Such products are increasingly in demand and may be mandated for use in factories or other commercial locations covered by strict environmental regulations. Such products are considerably more expensive to manufacture. Often, however, they are highly concentrated and at the final use dilution may not be excessively expensive to use.

More and more, high alkaline ore high acid cleaners are just not prudent options. Modern high efficiency systems utilize components that are less tolerant to the extreme formulations used in the past. The following sticker came from an air-handler manufactured by one of the largest equipment manufacturers. "To avoid damage to plastic pan, do not use strong cleaners (pH 9.5 or greater). Clean the coil with mild detergent & water. Rinse coil and pan thoroughly with clear water". The technician who ignores this label and uses an alkaline, acid or solvent based cleaner is taking a risk. That person may be open to a claim that they caused equipment damage or an IAQ problem. If it can be proven that they used an improper chemical, they could be liable for replacement of equipment or worse. Also interesting is the caution to, "Rinse…thoroughly with clear water." This raises a question about the cleaners that are marketed as "self rinsing" and rely on the condensate to remove soil loosened during cleaning. It is doubtful that such an approach can really remove all the soil.

The difficulty of removing heavy soils from inner coil fin surfaces has led some experts to recommend replacement of any coil that has not been maintained carefully since instillation and as a result is contaminated to the point where air flow is restricted below the manufacturer specifications. In the process of testing coil cleaners as part of product development, we cut a lot of coils apart following cleaning. Even after through cleaning, coils that appear clean on the surface still have noticeable organic material deposits on fin surfaces. These deposits contain spores that will grow when the coil becomes wet. Since these deposits are as much as an inch from the coil surface, it is impossible to tell by visual inspection if they are there following cleaning. We are still investigating the impact that such growths have on indoor air quality. Many feel they may be a major reason while problems are sometimes so difficult to eliminate. The more we learn about indoor air quality, the more we become convinced that a proper coil hygiene strategy is vital to any maintenance program.

Mr. Baker's field of expertise is the control of contamination in air-conditioning and ventilating systems by mold, mildew and bacteria. He writes and speaks frequently about the efficacy, legal risks, and regulatory issues involved in various control strategies. He serves on ASHRAE Technical Committee TC 2.3, TC 2.4, TC 9.8, and Sampling of Airborne Particulate Concentration in Commercial and Residential Buildings GPC 17P. He also serves as a member of ASTM D22.06 (Indoor Air Quality) and is on the Board of Directors of the Indoor Air Quality Association and the Florida Public Health Foundation. Because HVAC applications encompass new uses from an U.S. EPA regulatory standpoint, Mr. Baker works closely with the EPA and industry groups, including serving as the chair of the IAQ committee of the Consumer Specialty Products Association, to help formulate policy in this area.

Bob Baker is Chairman and CEO of BBJ Environmental Solutions, Inc., a company specializing in providing clean air through environmentally responsible products, such as BBJ MicroBiocide , BBJ Micro Coil Clean , "FreshDuct Odor Eliminator ", and BBJ Mold and Mildew Remover™ as well as the revolutionary new Power Coil Clean™. For additional information, Mr. Baker can be reached at (800) 889-2251 or through the company web site at http://www.bbjenviro.com.