Why Your A/C or Furnace Might Be Causing Water Damage — A Fast-Action Guide for Chicago Families

If you’re a busy parent in Chicago, Skokie, Evanston, Glenview, or Lake Forest, an unexpected water leak from your A/C or furnace can turn a normal week upside down. What starts as a small drip can quickly damage drywall, flooring, and insulation — and in many cases, mold begins growing within 48–72 hours.

The worst part?
Most HVAC-related water damage starts quietly, behind walls or in basements, before it becomes obvious.

In this guide, we break down:

• why HVAC systems leak in Chicago homes
• how to tell if water damage is already happening
• what to do immediately
• when to call a professional
• how to protect your home year-round

This guide is designed specifically for busy families — fast, clear, actionable.

Why HVAC Leaks Are So Common in Chicagoland Homes

Chicago’s climate is tough on HVAC systems. Here’s why your A/C or furnace is more likely to leak here than in other cities:

1. Freeze–Thaw Cycles Put Stress on Condensate Lines

Our winters drop below zero, then warm up again unexpectedly. This causes:

• frozen condensate lines
• hairline cracks
• blockages
• sudden thaw-and-dump leaks

2. High Summer Humidity → More Condensation

When your A/C runs constantly in July and August, it removes gallons of moisture from the air every day. If something is even slightly off in the system, water ends up on your floor—not in the drain pan.

3. Older Homes with Older Ductwork

Homes in Wilmette, Evanston, Oak Park, and Chicago’s North Side often have:

• outdated drain lines
• rusted pans
• older HVAC units
• less insulation

All of these increase the likelihood of leaks.

4. Finished Basements = Bigger Problems

Basements in Glenview, Highland Park, or Lake Forest may have:

• carpeting
• drywall
• built-ins
• kids’ playrooms

A slow HVAC leak behind walls can silently soak everything.

The Most Common Causes of A/C and Furnace Water Leaks

These are the issues we see most often in Chicago and the North Shore.

1. Clogged Condensate Drain Line

When the drain line is blocked with dust, dirt, algae, or debris, water backs up and spills into:

• basements
• mechanical rooms
• closets
• ceilings

This is the #1 cause of HVAC water damage in Chicago homes.

2. Cracked or Rusted Drain Pan

Older HVAC systems (especially 15+ years) often have rusted drain pans that:

• leak slowly
• overflow suddenly
• break completely

3. Frozen Evaporator Coil

A frozen coil melts all at once, causing:

• sudden water overflow
• soaked insulation
• ceiling leaks below

This is very common after Chicago cold snaps or when filters get clogged.

4. Dirty or Old Air Filters

When airflow is restricted, moisture condenses in the wrong places.

Busy families often forget filters — no judgment. It happens.

5. High Humidity and Oversized Units

Chicago summers are muggy.
If your unit is oversized, it turns on and off constantly, never fully dehumidifying the air — creating extra condensation and leaks.

6. Furnace Humidifier Malfunction

If you have a whole-home humidifier, a broken valve can leak a gallon an hour.

7. Improper Installation or Slanted Units

Even a slight tilt can cause water to drip in the wrong direction.

If you’re worried that your HVAC leak may have already caused damage behind walls or floors, make sure to read our guide on the 7 Hidden Signs of Water Damage in Chicago Homes— it walks you through exactly what to look for before small issues turn into major repairs.

How to Tell If Your A/C or Furnace Is Leaking — Before the Damage Spreads

Look for these subtle signs:

• musty odor near vents
• bubbling paint
• peeling drywall tape
• damp carpet around HVAC closet
• water pooling around the furnace
• rust stains on the unit
• higher humidity in one room
• hot/cold imbalance
• sudden spike in your utility bill

If you see any of these, water may already be inside your walls.

What Busy Families Should Do Immediately

Here’s the fast-action plan we recommend to parents juggling work, kids, and life:

1. Turn off the HVAC system

This stops water from cycling through the system.

2. Check around the unit with a flashlight

Look at:

• base of the furnace
• drain line
• drain pan
• surrounding floor
• nearby drywall

3. Replace the air filter

If it’s dirty, this may solve part of the issue.

4. Clean the drain line (if accessible)

A temporary DIY fix:

• pour warm water
• flush debris
• check for blockages

5. Watch for signs of mold

Mold grows fast in:

• basements
• closets
• utility rooms

If mold is already visible → call us immediately.

When You Should Call a Professional

You need a certified restoration team if:

• water is behind walls
• water soaked carpet
• water reached a finished basement
• you see mold
• the leak happened more than 24 hours ago
• you’re unsure where the water is coming from
• the same leak keeps happening season after season

Our IICRC-Certified team diagnoses the source, dries the structure, removes damaged materials, prevents mold, and restores your home.

We serve:

• Chicago (River North, Lakeview, Lincoln Park, Logan Square, Rogers Park)
• North Shore (Skokie, Evanston, Wilmette, Kenilworth, Winnetka, Glencoe)
• Lake County (Deerfield, Highland Park, Lake Forest, Lake Bluff)
• Northwest Suburbs (Mount Prospect, Arlington Heights, Palatine, Wheeling)
• Oak Park & River Forest

How ServiceMaster Restoration By Simons Helps Chicago Families Recover Fast

Families choose us because:

40+ years of local expertise

Serving Chicago, North Shore, Lake County, Oak Park & River Forest.

Nation’s oldest restoration brand (since 1929)

Born in Chicago.

IICRC Master Certified #137718

• Master Water Restorer
• Master Fire & Smoke Restorer

✔ IICRC Certified Firm #163465

✔ OSHA Registered (17-000173615)

✔ 24/7 emergency response

Leaks don’t wait for business hours.

✔ We work with families in mind

Clean, careful, respectful technicians.

✔ We prevent mold before it starts

This is huge for busy families who can’t risk weeks of disruption.

How to Prevent Future HVAC Leaks

1. Change filters every 30–60 days (families with pets: every 30)

2. Schedule HVAC tune-ups twice a year

3. Check the drain line at the start of each season

4. Ask your HVAC tech about a safety overflow switch

5. Don’t store boxes directly around your furnace

6. Keep a dehumidifier in the basement

When in Doubt, We’ll Take a Look

If you’re in:
Chicago, Skokie, Evanston, Wilmette, Glenview, Highland Park, Deerfield, Lake Forest, Oak Park, River Forest, Mt. Prospect, or Arlington Heights…

We can be there fast.

Call: (773) 376-1110
Or learn more:
https://servicemaster-restorationbysimons.com/restoration-services/residential/water

Worried the leak has already spread? Our full guide, 7 Hidden Signs of Water Damage in Chicago Homes, explains exactly what to look for so you can act fast.

About ServiceMaster Restoration By Simons

ServiceMaster Restoration By Simons is Chicago’s trusted water, fire, and mold restoration company with 40+ years of local service across Chicago, the North Shore, Lake County, and Oak Park/River Forest. Led by CEO Nasutsa Mabwa and COO Sam Simon (IICRC Master Restorer #137718), our team has earned:

• 2025 Inc. 5000 Honoree
• BBB Torch Award
• Chicago Star Award
• SB100 Best of Small Business
• Stevie Award

We are fully IICRC-Certified (Firm #163465) and OSHA-registered (17-000173615).

Internal Resource Links

Core Services

• Water Damage Restoration:
  https://servicemaster-restorationbysimons.com/restoration-services/residential/water
• Fire Damage Restoration:
  https://servicemaster-restorationbysimons.com/restoration-services/residential/fire
• Mold Remediation:
  https://servicemaster-restorationbysimons.com/restoration-services/residential/mold
• Specialty Cleaning:
  https://servicemaster-restorationbysimons.com/restoration-services/residential/specialty

FAQs

Q1: Is water leaking from my furnace dangerous?
Yes. It can cause electrical hazards, mold growth, and hidden structural damage.

Q2: Why does my A/C leak more in the summer?
Chicago’s high humidity creates heavy condensation. If the system is dirty or clogged, it leaks.

Q3: Can HVAC leaks cause mold?
Yes — mold begins growing in 48–72 hours.

Q4: Should I call HVAC or a restoration company first?
Call restoration first if water is present — HVAC techs don’t dry structures or remove wet materials.