There are two basic types of coils that are used to transfer heat either in or out of air streams.

1. Condenser coils. Transfers heat into a space. Refrigerant vapor is forced into the coil under pressure, condensing the refrigerant into a liquid, which results in the rejection of heat across the heat exchange surface.

2. Evaporator coils - Do the opposite to condenser coils. Liquid refrigerants is pumped into a low pressure coil, causing the refrigerant to evaporate into a vapor, absorbing heat across the heat echange surface in the process.

Like most things, the surface of these coils can become dirty as the air moves over the coils. The air carries dust, dirt, pollen, moisture and other contaminants. With these contaminants building up on the surface area, it reduces the efficiency of the heat transfer process, leading to excessive energy consumption and poor system performance. It is necessary for the coils to be regularly inspected to ensure that they are operating at maximum efficiency. With the help of regular coil cleaning, the life span of the equipment and indoor air quality improves dramatically.

According to the US Department of Energy (DOE), "a dirty condenser coil can increase compressor energy consumption by 30%". A dirty evaporative coil will decrease airflow which reduces heat transfer thereby degrading the dehumidification process.

When to clean the coils. Looking at the difference between a dirty coil and a clean coil is one way to indicate when you'll need cleaning. The other way is more technical and requires measuring the temperature difference between the air entering and the air leaving the coil. As such, this testing should be carried out by a professional or experienced service provider. Cleaning should be carriout out by a professional as well to ensure that the equipment is not damaged or contaminated during the cleaning process.