How to Clean Your HVAC System with Coil Combs, Chemicals, or Ultraviolet Light

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Cleaning evaporator coil on your HVAC system to improve indoor air quality

There are several ways to save energy and maintain the Indoor Air Quality, IAQ, of your home. The best way to accomplish both is by keeping the evaporator coil in your air handling unit clean.

Higher operating pressures and temperatures caused by a dirty coil can cause a serious problem: reduced life expectancy of the equipment. At the elevated system temperature and pressure, the compressor's lubricating oil can break down. In addition, acid formation can occur, leading to an acid burnout. With the lack of lubrication and acid burn, the compressor is seriously compromised and will fail prematurely. It is the main component of an air conditioning system, and its loss means no cooling. Its replacement is the most expensive repair on an HVAC system.

Evaporator Coil

As evaporator coils cool indoor air, it also dehumidifies the air. Any dirt, dust, nicotine, pollen, etc. that is also in the air will combine with the moisture and eventually foul the coil. Once this occurs, two problems arise: air flow is reduced and heat transfer is reduced. This can not only damage the compressor, but also reduces the effectiveness and comfort level of your home. With less efficient heat transfer, the unit will need to stay on longer to maintain the temperature setting, consuming more energy. Replacing or cleaning the unit’s filters can reduce energy consumption by 5 to 15%. You can also save over $300 annually on a typical 4-ton air conditioning unit by keeping your evaporator coil clean.

You should consider the condition of the evaporator coil, commonly called an A-coil due to its shape, inside the air handling unit. This is the coil that cools the air and is located after the filters. If not cleaned regularly or the filters are not changed every 6 months, the coil may be too dirty to effectively cool the air and would therefore waste energy. Dirty evaporator coils can reduce cooling capacity from 25 to 30%, this would be like replacing your 4-ton unit with a 3-ton unit.

You should clean the evaporator annually with a vacuum and a fin comb. Combing the fins on the coil will remove the build up of dirt and grime. These tools may come with single, multiple or interchangeable heads that have different comb sizes and counts to best match the coil fin size of the A-coil. Some six sided head models will work for 8, 9, 10, 12, 14 and 15 fins per inch coils. The comb is carefully drawn across the bent coil fins straightening them out in the process. Fin combs can be purchased at refrigeration supply houses or online. A set comes with various sizes and usually costs less than $10.

Fin combs

You can also clean the coil with a foaming coil cleaner. These types of cleaners have chemicals which dissolve the dirt, but are safe for the coils. If you purchase self-rinsing coil and fin cleaners it is not necessary to rinse the coil of the unit since moisture produced will rinse product from contacted surfaces. Only use cleaners that say that they are “Nickel-Safe.”

Another alternative would be to install a UVC air purification solution. These kits are comprised of a mounting bracket, power converter, and UVC light which is inserted into the side of the unit on the downstream side of the evaporator coil. The light breaks down all organic material it is exposed to and keeps the coil extremely clean. This not only saves energy, it also kills germs and viruses inside the unit. The kits can be installed professionally or by the homeowner; caution should be used since the light generated by the bulb can break down coatings on any wiring that is not rated for UV exposure. Follow the directions provided by the manufacturer.  A UVC unit can also be placed further downstream from the unit in the center of the supply duct to kill mold, spores, viruses, and other volatile organic compounds. (VOC)

UVC light for residential units

Condenser Unit

The condenser coil (Outdoor section) should be cleaned annually in the spring prior to the cooling season. Make sure that you remove any leaves and debris that have collected in and around the unit. Trim back any branches or shrubbery at least 2 feet on all sides. You can try vacuuming the coils and use the fin comb again to straighten any crushed coils, or use your garden hose to blow out any dirty inside the fins. Don’t use a pressure washer as these could compress the fins if you use too powerful of a stream.

Always make sure you have the power shut off to the units before you begin work. Read and understand the Operation and Maintenance manual for your unit before you begin working as well.