WHY ARE MY EVAPORATOR COILS LEAKING?

Understanding How Hydrogen Peroxide-Based Disinfectants Can Damage Copper Coils

By Southeast Coil Pro

The Question We Hear All the Time:

At Southeast Coil Pro, we’re often asked:

“Why are my evaporator coils leaking — especially when they’re only a few years old?”

After decades of working with commercial HVAC systems, we’ve seen nearly every cause of

coil failure — from formicary corrosion and poor installation practices to environmental

exposure in tough industrial settings. But in recent years, we’ve identified a new and fast-

acting culprit: hydrogen-peroxide-based disinfectants.

These products became common during the COVID-19 pandemic, when many facilities

began fogging or misting rooms to sanitize surfaces and air. Unfortunately, what’s good for

disinfection can be very bad for copper.

Common Causes of Coil Leaks (and What’s Changed)

Before diving into hydrogen peroxide corrosion, here’s a quick look at other leak causes we

often encounter:

• Improper installation: Not using backup wrenches or over-torquing connections can

stress copper stub-outs and lead to early leaks.

• Formicary corrosion (“Ant’s Nest Corrosion”): Caused by organic acids, off-gassing

materials, or contaminants from drywall and cleaning agents.

• Environmental exposure: Food-production facilities, swimming pool areas, and coastal

environments often emit corrosive vapors that attack copper.

For example, one national food manufacturer we helped had multiple coil failures due to

airborne propionic acid from a baking process. Our solution — custom stainless-steel tube

coils with protective coatings — solved the issue long-term.

But lately, even in clean, climate-controlled spaces, we’ve seen a rise in pitting corrosion

and rapid leaks in relatively new coils. The common denominator? Hydrogen peroxide

fogging.

How Hydrogen Peroxide Damages Copper Coils

Hydrogen peroxide (H₂O₂) is a strong oxidizer. When it contacts copper, it reacts aggressively and strips away the metal at a microscopic level.

Here’s what’s happening behind the scenes:

1. Oxidizing Action — H₂O₂ converts metallic copper into oxides (Cu₂O, CuO), slowly thinning the tube walls and creating weak spots.

2. Fenton-Type Reaction — In the presence of copper, peroxide generates reactive hydroxyl

radicals (•OH) that cause deep, localized pitting.

3. Peracetic Acid Blends — Many commercial sanitizers combine hydrogen peroxide with peracetic acid or stabilizers. Peracetic acid is even more corrosive to copper and brass.

4. Environmental Factors — High humidity, heat, or chloride residue accelerate the process. Fogging residues left on fins trap moisture and create micro-environments where corrosion concentrates.

How Coil Failures Show Up in the Field

1. External pitting on finned tubes — Repeated fogging cycles cause corrosion where tubes

meet fins, especially in moist evaporator coils.

2. Leaks at brazed joints and headers — Oxidizers attack flux residues or gaps at brazed

seams, leading to leaks near joints or manifolds.

3. Internal corrosion in water coils — Some facilities also add peroxide to closed water

loops for sanitation. If not carefully controlled, this can corrode copper tubes from the

inside out.

4. Fast failure in DX coils — Direct-expansion (DX) coils have thin tube walls. Even minimal

pitting can cause refrigerant loss and force complete coil replacement.

Real-World Examples from the Field

During and after the COVID-19 pandemic, we inspected dozens of facilities and saw the

same trend across industries:

• Hospitals and healthcare centers – used vaporized hydrogen peroxide (VHP) for

sterilization.

• Hotels, convention centers, theme parks, and schools – adopted fogging for frequent

disinfection.

• Pharmaceutical and cannabis production facilities – used peroxide fogging to maintain

cleanroom standards.

All reported premature coil corrosion with the same signature blue-green copper oxidation

and pinhole leaks. In nearly every case, hydrogen peroxide or peracetic acid disinfectants

were the root cause.

How to Spot the Warning Signs

Watch for these indicators of peroxide-related coil damage:

• Green or blue corrosion on return bends or headers

• White powdery residue on fins or tubes

• Repeated coil leaks or refrigerant loss with no mechanical damage

• Leaks near brazed joints or manifold connections

How to Prevent Coil Corrosion from Fogging

1. Review Your Disinfectant’s MSDS — Check for ingredients like hydrogen peroxide or

peracetic acid.

2. Protect or Isolate Coils During Fogging — Cover AHU coils, seal intakes, or bypass

systems during fogging cycles.

3. Use Lower Concentrations and Shorter Cycles — Work with your infection-control team

to balance effectiveness with safety.

4. Choose Corrosion-Resistant Materials — Consider stainless steel, copper-nickel, or

epoxy-coated coils for high-sanitation areas.

5. Inspect and Maintain Regularly — Add visual inspections and monitor leak frequency

after fogging events.

The Bottom Line

Hydrogen peroxide–based disinfectants were essential during COVID, but they can also be

highly corrosive to copper coils. If your evaporator coils are leaking prematurely, hydrogen

peroxide exposure could be the hidden cause.

At Southeast Coil Pro, we’ve helped hundreds of facilities identify, repair, and prevent these

types of failures. Our team provides forensic coil analysis, custom coil replacements, and

protective coatings to extend coil life.

Need Help with Coil Leaks or Corrosion?

Contact Southeast Coil Pro today for expert guidance on diagnosing and preventing coil

damage.

sales@southeastcoilpro.com

877-COIL-411

www.southeastcoilpro.com

Southeast Coil Pro – Engineered Solutions for Coil Longevity – DESIGN – REPLACE -

PROTECT