What Causes Formicary Corrosion?

Indoor coil leaks in HVAC systems have been an industry-wide problem for decades. The primary cause of these leaks is a phenomenon known as formicary corrosion. It affects copper-based alloys and is unobservable to the unaided eye. The term “formicary” literally means “ant’s nest.” Similar to an ant’s nest, corrosive tunnels form inside copper tubing which ultimately causes leaks.

The standard industry copper alloy used in indoor coils can form leaks within three years of installation in highly susceptible regions of the country. The problem is most prominent in regions with particularly high humidification levels. Standard copper coil life expectancy varies depending on organic acid formed, and how quickly it can make it through the copper grain to form a hole.


The presence of four elements leads to formicary corrosion. If any ONE factor is eliminated, the corrosion can be prevented. These elements are copper, moisture, oxygen and acid. The combination of these elements leads to formicary corrosion.

Copper – Indoor coil is an essential component of a central air conditioner and heat pump system. Copper tubing is by far the most common material used to make these coils.

Moisture – Beads of condensation collect on the coils inside the HVAC system. This moisture can create a fertile environment for formicary corrosion. Southern markets see the highest incidence of formicary corrosion because moisture is typically present on the coil year-round.

Oxygen – It’s in the air we breathe and is an essential element for all organic life. When combined with the other necessary elements, it can cause formicary corrosion.

Acid – Environmental contaminants such as household particles collect on the copper tubing and mix with the moisture. This forms an organic acid that begins to eat away at the copper. The acid creates a tunneling effect similar to that of ant tunnels, penetrating the copper completely and creating the leak.

Building materials, household cleaners, carpet chemicals, acidic foods and adhesives and many other common household items all contribute to formicary corrosion. It is nearly impossible to control these airborne particles just as it is to prevent moisture from forming in a high-humidity environment.

Preventing Formicary Corrosion

In order to prevent formicary corrosion, one of the four component elements must be eliminated. It’s practically impossible to remove oxygen, moisture and acid from the environment. That just leaves copper. HVAC systems that utilize aluminium coils, such as the Anteater MC Micro-Channel, take copper out of the equation. Without the the presence of copper, formicary corrosion cannot occur.