What Causes Formicary Corrosion and How to Prevent It
If you’ve ever dealt with a leaky HVAC coil that seemed to fail far too early, you may have encountered a silent culprit known as formicary corrosion. This little-known type of damage can cause significant problems, particularly in copper-based HVAC components.
But what exactly causes it—and more importantly, how can it be stopped?
Alamo Austin Air explore the science behind formicary corrosion, where it comes from, and what you can do to prevent it.
What Is Formicary Corrosion?
According to industry studies, formicary corrosion is responsible for around 10% of early copper coil failures in the HVAC industry. That may sound like a small number, but considering the cost of repairs and refrigerant loss, it’s a major concern for Austin, homeowners and HVAC professionals alike.
Formicary corrosion, sometimes called ant-nest corrosion or pinhole corrosion, is a type of chemical corrosion that affects copper-based alloys, such as the tubing used in many residential and commercial HVAC systems.
It gets its nickname from the microscopic maze-like patterns that resemble an ant nest when viewed under magnification.
Unlike more visible types of corrosion, formicary corrosion is not usually detectable with the naked eye. You might notice some gray, black, or bluish discoloration on the surface of copper tubing, but the real damage happens internally.
Over time, this hidden damage can cause small leaks, particularly in HVAC coils, that may go unnoticed until the system’s performance worsens or refrigerant leaks out.
What Causes Formicary Corrosion?
Formicary corrosion occurs due to a chemical reaction involving three components:
- Oxygen
- Water (moisture)
- Organic acids (particularly formic and acetic acids)
When these elements are present simultaneously and come into contact with copper, they can slowly eat away at the metal, creating tiny channels and holes. These organic acids are the most unique and preventable part of the equation.
So, where are they coming from?
Sources of Organic Acids That Cause Formicary Corrosion
The surprising answer is where the organic acids come from: your everyday household items, such as:
- Adhesives and caulks
- Cabinets and particleboard
- Foam insulation
- Oil-based paints and latex paints
- Wallpaper and vinyl flooring
- Cleaning solvents and disinfectants
- Vinegar
- Cosmetics
- Tobacco smoke
- Wood smoke
These materials and products release volatile organic compounds (VOCs), harmful gases that can contribute to indoor air pollution. Over time, these VOCs can break down into organic acids, like formic and acetic acid, which contribute to corrosive corrosion.
The U.S. Environmental Protection Agency warns that indoor VOC levels can exceed safety limits, especially in newer, tightly sealed homes with limited fresh air ventilation. This puts these homes at a higher risk of experiencing formicary corrosion.
How Does It Affect HVAC Coils?
Formicary corrosion most often affects copper HVAC coils, which transfer heat in air conditioning and heat pump systems. If the acids come from the air inside your home, they can attack the outside of the coil tubing.
A manufacturing defect or contamination might be present inside the sealed system, though this is far less common—less than 10% of cases.
Can It Harm People or Pets?
The answer is yes. At high enough levels, formic and acetic acid vapors can be harmful to humans and animals.
Exposure over five parts per million (ppm) may lead to eye, throat, and respiratory irritation, and at higher concentrations, there can be more serious effects like central nervous system symptoms or damage to lungs and eyes.
While these levels are relatively high, they highlight the importance of managing indoor air quality, not just for your HVAC system but also for your health.
How Can Formicary Corrosion Be Stopped?
The good news: there are practical steps you can take to reduce the risk of formicary corrosion in your home.
1. Identify and Minimize VOC Sources
Look closely at what products you use around the house, especially near return air vents and HVAC systems. Switch to low-VOC or VOC-free alternatives whenever possible.
Read product labels carefully, especially for things like:
- Household cleaners
- Paints and solvents
- Plywood or pressed wood furniture
- Air fresheners and deodorizers
In newer homes, be aware that construction materials like insulation, cabinets, and caulking may still be off-gassing VOCs long after installation.
2. Improve Ventilation
One of the most effective strategies for reducing indoor VOC levels is to increase the amount of fresh air brought into your Austin home. This is where systems like heat recovery ventilators (HRVs) or energy recovery ventilators (ERVs) come in.
These systems help exchange stale indoor air with fresh outdoor air while maintaining energy efficiency. Although it hasn’t been scientifically proven that increased air exchanges directly prevent formicary corrosion, the EPA recommends this strategy when using VOC-emitting products.
The idea is simple: reducing the concentration of organic acids in the air can reduce the chances of corrosion.
3. Work With a Professional HVAC Contractor
A licensed HVAC technician from Alamo Austin Air can help assess your system and indoor air quality. If coil corrosion is suspected, they can help identify whether it’s formicary corrosion or another issue and advise on the next steps.
Sometimes, testing at the original equipment manufacturer’s lab may be necessary for a definitive diagnosis.
If a replacement is needed, some newer coils use aluminum or coated copper to reduce the risk of corrosion.
Contact Alamo Austin Air if You Suspect Formicary Corrosion
Formicary corrosion is a sneaky but serious threat to HVAC systems, especially in modern, tightly sealed homes filled with VOC-emitting products. While the damage it causes is hidden from view, the results can be costly.
By understanding what causes this type of corrosion and taking steps to improve your indoor air quality, you can extend the life of your HVAC equipment, protect your investment, and breathe easier—literally.
Need help improving your home’s air quality or suspect HVAC coil damage? Contact Alamo Austin Air, your trusted HVAC contractor in Austin, today for an inspection and professional advice. Call 512.265.0465 or request service online.