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formulation would have to be exactly pH 7 to be truly neutral and detergent cleaners generally fall in a range between pH 4 and 9. Important Note: Sometimes, cleaners are formulated for specific types of soils. For example, systems that serve commercial kitchens may have greasy soil that requires a special formulation. In addition, regional conditions may favor one cleaning formulation over another. It is normal for contractors to select coil cleaners by trial, eventually settling on one or two formulations that work best for the conditions that they encounter. User and occupant safety is a critical issue and cleaners at both ends of the pH range tend to be unpleasant to use and handle. Typical use Traditionally, acid cleaners are used on condenser coils because the types of soils that are associated with their outside location are more easily removed by the acid formulation. In a like manner, alkaline cleaners sometimes work better with the greasy soil that is often found on indoor evaporator, chilled water, or heat pump coils. Because both of these cleaner types can be unpleasant to use and can damage coil surfaces, there has been a trend toward greater use of detergent cleaners. Acid cleaners should never be used indoors as they release unpleasant and potentially dangerous fumes unless rinsed completely from all surfaces in the air handler. Coil cleaners are normally used for cleaning other portions of an HVAC system such as fans and housings, drain pans, supply and return grills and supply plenums that have an accumulation of soil and microbial growth. In special situations such as following a fire, an entire duct system may have to be cleaned with a detergent cleaner. Application method Each manufacturer develops directions for the use of its cleaners, and in many cases these directions are based on actual research findings. For this reason, a user should always refer to the directions printed on the container label as the best way to effectively use the product. The following are generally applicable to all coil-cleaning compounds: n Prepare the proper use dilution: The product label should recommend a starting-use dilution. A common dilution is one part cleaner to three parts water. In most cases water from the tap is acceptable. n Apply to coil: Dilute cleaner can be applied with a hand sprayer or a power sprayer. In most situations, a power sprayer – not to exceed 150 psi - provides better coverage and deeper penetration into the depth of the fin assembly. Several sprayers are manufactured specifically for coil cleaning and have enough power to penetrate, yet not enough to damage or bend the fins. Spraying directly facing the fins rather than across fins will result in less damage. Cleaner should be sprayed from side to side onto the coil assembly, starting from the bottom and working to the top. This allows loose soil to rinse out of the coil assembly as you proceed rather than falling down the fins and becoming more impacted. n Allow soaking time: The soil-removal activity of most cleaners takes time so the cleaner should not be rinsed off too soon. Four to five minutes is a good general soak time. However, do not let the cleaner dry on the coil surface or it may be difficult to rinse off. Some coil cleaners are marketed as 'no rinse' as the condensate is supposed to wash the residue off. If a coil is cleaned during a dry time of year, that does not happen since there is little or no condensate. Pros n The soil that accumulates on coils (especially cooling coils) is extremely difficult to remove. Unless a coil is cleaned very frequently, it is virtually impossible to remove the soil without using some cleaning compound. n Cleaners speed up soil removal and thus less labor is needed for coil cleaning. n More complete cleaning results in significant energy savings. n Complete cleaning lowers the possibility of bacteria and fungi growing on coil surfaces being carried to occupied spaces. Cons n Use of a cleaner risks exposure to chemicals that may be toxic or irritating to users and occupants. n Some areas have regulations preventing the discharge of cleaning compounds (especially alkaline cleaners) into storm sewers or roof drains. n Some cleaners (extremely high and low pH) can damage and shorten the life of the coils. EPA Requirements The EPA does not have the authority to regulate cleaning compounds. However, in the spring of 2010, the EPA published a notice that they had received reports of cleaners that are being marketed with claims that they "remove microbial growth." If marketers make such claims, those products will be regulated as antimicrobial pesticide products. Thus, it is important that service providers and sellers of coil-cleaning compounds not make any claims related to microbial growth control, prevention, or removal as this would make their product subject to registration by the EPA.