HVAC Coil Cleaning:



Before                                 After


One of the best ways to cut your air conditioning bill is to keep your AC coils clean and running efficiently.  You can cut your energy costs by up to 30% with yearly cleanings.  You also save on costly service calls for frozen up units with preventative cleaning to ensure you are running at 100% efficiency.


Cleaning both the condenser and evaporator coils is an extremely important part of maintaining your HVAC systems.  With the condenser most commonly placed on the roof of your business, it is exposed to grease from the kitchen exhaust fans, cottonwood, and all sorts of physical pollution.  When this debris collects on your condenser coils it puts a strain on your HVAC equipment up to and including failure of some serious mechanical parts.  When you consider the cost of replacing just one compressor would cover the cost of cleaning that same HVAC unit for up to five years it’s easy to see the benefits of our semi-annual HVAC PM program. 

For any system to run at its optimum performance, clean coils are extremely important. Clean coils positively affect energy efficiency, indoor air quality and long-term system performance. With dirty coils, all three of these elements suffer. Here is a look at how to keep air-cooled systems running smoothly.


An air-conditioning system has two finned coils, usually made of copper tubes with aluminum fins. The evaporator coil is the indoor coil and it's often described as the “cold” coil because it provides indoor cooling by absorbing heat from the building air blown over it by a fan. The condenser coil or outdoor coil is the “warm” coil as it rejects the heat as a fan blows outside air over it.


The coils are sized to match the Btu cooling load of the building and they are engineered for maximum heat transfer. This maximum heat transfer is dependent on having clean coils. Unfortunately, the air moving over the coils contains dust, dirt, pollen, moisture and other contaminants so the coils get dirty.


Even though the evaporator coil is protected with an air filter (the condenser coil does not have this protection), over time they still get dirty. In addition, the evaporator coil and its condensate pan can become fouled with pollen, mold spores and other biocontaminants, all of which can have an adverse effect on indoor air quality. With all the moisture around the evaporator coil, it can become a breeding ground for bacteria and mold.

The costs of dirty coils



A coil fouled with dirt and grime cannot supply proper heat transfer, which results in higher discharge pressures and greater energy consumption. Equipment operating with dirty coils can use up to 37 percent more energy than it does with clean coils.


Accumulating dirt on coils inhibits heat transfer, which makes the compressor work harder, adding more heat and raising head pressures as much as 75 percent. Higher head pressures reduce the system's cooling capacity by as much as 30 percent, a condition that is most noticeable on the hottest days when cooling is required the most.


The higher temperatures and operating pressures caused by dirty coils can shorten the life of the equipment by leading to the breakdown of the compressor's lubricant. Acid formation also can occur under these conditions, leading to an acid burnout. Acid formation and lubricant breakdown will adversely affect the compressor, leading to equipment failure. A failed compressor means no cooling and costly repair.


A dirty coil reduces the cooling ability of the air blowing across the condenser coils. If the condensing temperature is raised from 95° Fahrenheit (F) to 105°F as a result, then cooling capacity will be cut by 7 percent and increase power consumption by 10 percent, with a net compressor efficiency reduction of 16 percent. Such performance degradation in a 10-ton unit operating at 9.0 EER for 2,000 hours per year at 8 cents per kilowatt-hour wastes about US$250 per year in operating costs (Figure 1). It takes a technician about an hour to clean the condenser, which typically costs about $50 and up. This is money well spent—in this example, cleaning the unit would have a payback of just over two months, with a net annual savings of $200.


Typically when a HVAC contractors make the effort to service a unit, several tasks are performed, including cleaning the dampers and both the condenser and evaporator coils, changing the filters, tightening belts, inspecting and servicing the fans, and verifying refrigerant charge levels as well as damper and economizer functionality. The cost for an annual maintenance contract that includes all of these tasks is between approximately $1,000 and $1,200 for a 10-ton unit. Filter changes and inspections are frequently performed quarterly, with the remaining tasks performed annually.


Although the energy savings achieved from cleaning the condenser coil alone won’t cover the cost of an annual maintenance contract, the other services performed will also deliver savings. More importantly, these services will ensure that the unit cools the building and its occupants as intended. Also, they will help to prevent or quickly catch malfunctions before they have a chance to further degrade the equipment or waste significant amounts of energy. An economizer stuck in the open position in a climate such as that of Tampa, Florida, for example, can cause the HVAC system to use 50 percent more energy than a system without an economizer.



The condenser coil is exposed to unfiltered outside air and elements such as dust, dirt, leaves, grass clippings, animal fur, animal urine and more. While the condenser coil does not affect indoor air quality, cleaning it at the same time as the evaporator coil will result in improved energy efficiency.

A coil cleaning program should be instituted when the coils are new and clean, and should be performed with enough frequency to prevent coil deterioration. This can be as often as four times a year (monthly cleaning is reported in some areas).


If they do not already exist, install easy-to-open panels to gain access to the coils. This will make the job much easier and, consequently, the job is more likely to be done when necessary.


Traditional cleaning methods



There have been several methods employed for cleaning the fin surface of the coils over time. If the coil is contaminated with only a light dust or dirt that does not strongly adhere to the fins, blowing low-pressure compressed air across the fins or using a soft bristle brush, or both, may be sufficient.


Another method is to apply plain water or mild detergent solution to the surface, allowing it to sit for a short time and then rinsing it off. More aggressive deposits call for the use of stronger cleaning solutions or solvents as required.


It is important that these solutions are chemically compatible with the coil construction to avoid damaging the fins and other coil components. Solutions must also be monitored with a view to avoid damage to surrounding surfaces and shrubs.


Coils also can be steam cleaned but extra care is called for when doing so. The steam must be applied at low pressure and the steam stream kept parallel to the fins to prevent folding the fins over. In cases where the fin–to–tube interface is badly corroded, steam cleaning can cause further deterioration.

Another popular cleaning method employs the use of a garden-type pump sprayer to apply foaming chemical to the coil surfaces. The foam is allowed to dwell on the surface for a specific time period. The foam is then vacuumed up and a second application and vacuuming is performed. Finally, the coil is rinsed with clean water from a hose while excess water is collected by vacuum.


Perhaps the most popular cleaning method used today is pressure cleaning the coils. Pressure cleaning coils may increase airborne macromolecular organic dust (MOD), which must be contained to the area being cleaned. Plastic sheeting attached with duct tape will prevent contamination of duct entries. 

Whenever possible, pressure cleaning should be done in the opposite direction of airflow. This helps prevent packing the contaminants further into the center of the coil. A cleaning solution can be applied before the pressure rinse using the built-in chemical injection system on the pressure washer or a hand sprayer.


Care must be taken when using a pressure washer to avoid damaging the fins on the tubes. This may require keeping the spray nozzle some distance from the surface. It is also recommended that the spray should contact the coil at a 45-degree angle. This enhances the breakdown and removal of contaminants, as well as preventing the compaction of debris deep into the coil. Water leaving the coil should be free of particulate. If it is not, repeat the process.


Pressure washing uses a significant volume of water so care must be taken to avoid flooding the work area. Make sure the condensate drain pan drain line is open and flowing freely before beginning.


About chemicals

There are many acid and alkaline-based cleaners available for coil cleaning today. These chemicals clean by creating a chemical reaction between the cleaner and the metal, but this harms the surface of the metal. In turn, it damages the coils by causing metal loss over time.


Furthermore, acid and alkaline-based chemicals carry with them an inherent danger to personnel and equipment. Extra care and the use of appropriate protective equipment are called for to prevent chemical burns and other accidents.


The foaming properties of many coil cleaning formulations are important to help float debris out of the coil body where it can be rinsed away.


While some chemicals are advertised as “no rinse,” many believe that all cleaning chemicals should be thoroughly rinsed from the surface to prevent coil damage. Newer chemicals available today offer non-acidic, nontoxic, odorless formulations that perform as well as more hazardous cleaners. 


Call Boston Environmental today to schedule to have your coils washed. Prices start at $145.00