Why Your A/C Might Be Causing Water Damage Inside Your Walls — And How to Stop It Before It Spreads

The Hidden Danger of HVAC Condensation in Chicago Homes

Every summer, Chicagoland homeowners crank up their air conditioners to combat sweltering heat and sticky humidity. But what many don’t realize is that overcooling your home without managing indoor humidity can lead to a serious threat: hidden water damage from A/C condensation.

This type of damage often occurs behind walls, inside ceilings, and around ductwork—places you can’t easily see until it’s too late. And if you live in a historic home or an older high-rise with minimal insulation, you're especially at risk.

How Air Conditioning Systems Create Hidden Moisture

Air conditioners cool your home by pulling moisture from the air. That moisture, in the form of condensation, is supposed to drain away through your system’s condensate line. But when ductwork or pipes run through poorly insulated wall cavities, the cool surfaces of those ducts can “sweat” excessively.

“One of the most common HVAC-related water damage issues we see during Chicago summers is condensation on ductwork and water pipes—especially those hidden behind walls and ceilings,” explains Sam Simon, IICRC Master Fire & Water Restorer and owner of ServiceMaster Restoration By Simons. “Exposed ducts are usually fine, but when those cool surfaces are trapped inside unventilated wall cavities during a heatwave, they can sweat constantly—and that moisture has nowhere to go.”

Real-World Case: Bucktown Home with Ceiling Mold

“We had a case in Bucktown where a family noticed mold starting to form on a ceiling, but they couldn’t recall any water event,” says Simon. “Our thermal camera showed cold ductwork running directly through that section of drywall. Once we opened it up, the duct was soaked—covered in condensation. Outside temps were in the 90s, and the A/C had been running nonstop for days.”

This is a common situation in neighborhoods like Bucktown, Logan Square, West Town, and even North Shore suburbs like Evanston and Wilmette—especially in vintage homes with upgraded but poorly insulated HVAC systems.

Why Older Homes Are at Higher Risk

Chicago has a large inventory of pre-1950s homes that were never designed for modern central air. These homes often have:

• Thin or absent insulation
• Wall-mounted or attic ductwork retrofits
• Shared ventilation systems
• Plaster walls that conceal moisture until mold sets in

“Older homes in Chicago weren’t built with insulation in mind,” Simon notes. “That means warm, humid air easily seeps into wall cavities and meets cold ductwork or pipes. That contact creates instant condensation—and if it’s left unchecked, it leads to mold growth and structural water damage over time.”

Signs of HVAC-Related Water Damage to Watch For

Since this type of damage is hidden behind walls or ceilings, you’ll need to rely on subtle clues:

• Bubbled or blistered paint
• Soft spots in drywall or ceilings
• Unexplained mold growth
• Musty odors in rooms with vents
• Dripping sounds with no visible source
• Water stains around vents or along baseboards

“These types of hidden water intrusions are hard for homeowners to catch early,” Simon adds. “Unless you notice discoloration in the paint, softness in the drywall, or patches of mold, you wouldn’t even know it’s happening.”

Why Chicago’s Humidity Makes It Worse

In summer, humidity levels often exceed 70–80% in Chicagoland. Combined with A/C systems pushing air down to 60–65°F, the delta between indoor and outdoor conditions creates ideal conditions for condensation.

Even worse? Basements, attics, and crawl spaces act like moisture traps, amplifying the problem.

What Happens If It’s Left Untreated?

Unchecked HVAC condensation can lead to:

• Mold growth inside walls
• Rusted or rotted metal ducting
• Wood rot and structural weakening
• Electrical hazards (condensation near wiring)
• Reduced air quality and health risks
• Damage not always covered by insurance

How to Prevent HVAC Condensation Water Damage

“My top recommendation is simple: run a dehumidifier on hot, humid days,” says Simon. “Chicago summers are muggy. Lowering your indoor humidity is one of the best ways to prevent condensation from forming inside your walls and ceilings.”

Here are 7 proven ways to reduce the risk:

1. Use a dehumidifier in basements, crawl spaces, or entire homes
2. Insulate ductwork and cold water pipes—especially in wall cavities or attics
3. Seal air gaps around vents, chases, and attic openings
4. Install vapor barriers behind drywall in problem areas
5. Service your HVAC system yearly to ensure drainage is working
6. Keep your home’s relative humidity under 50%
7. Use smart thermostats to avoid overcooling your home

What to Do If You Suspect a Problem

If you notice any signs of hidden water damage, don’t wait. Moisture problems can escalate rapidly during a Chicago summer.

At ServiceMaster Restoration By Simons, we use:

• Thermal imaging and moisture meters to locate hidden water
• Professional drying equipment to eliminate trapped humidity
• Mold remediation protocols if microbial growth has begun
• Full-service restoration, including drywall replacement and duct cleaning

Areas We Serve

We proudly serve homes, condos, and businesses across:

• Chicago neighborhoods: Bucktown, Lincoln Park, Lakeview, Gold Coast, Wicker Park, Rogers Park, Humboldt Park, Logan Square
• North Shore suburbs: Evanston, Skokie, Wilmette, Winnetka, Glencoe, Glenview, Northbrook
• West Suburbs: Oak Park, River Forest, Elmwood Park, Forest Park, Addison, Naperville
• Lake County: Highland Park, Lake Forest, Lake Bluff, Deerfield, Vernon Hills, Libertyville

Final Thoughts

Your air conditioner may be keeping you cool—but it could also be quietly causing expensive water damage behind your walls. With Chicagoland’s intense humidity and aging housing stock, it’s never been more important to stay proactive.

Don’t let condensation become a costly surprise. If you suspect moisture behind your walls or around ductwork, call the trusted experts at ServiceMaster Restoration By Simons.

Call Now for Expert Water Damage Restoration

Chicago: (773) 376-1110
North Shore: (847) 316-9145
Oak Park & River Forest: (708) 524-0304

Also Recommended:

RESTORE: A Complete Guide To Protecting Your Home As Your Most Valuable Asset
Co-authored by Sam Simon, this essential homeowner guide includes chapters on hidden water damage, mold, and HVAC issues.

Related Services

• Residential Water Damage Restoration
• Mold Remediation
• Air Duct & HVAC Cleaning
• Commercial Restoration Services
• Fire Damage Restoration