How Flood Damage Affects Your HVAC System Years Later
When floodwaters recede, the immediate focus is on the visible damage — ruined flooring, soaked drywall, destroyed furniture. Your HVAC system, if it still powers on and blows air, gets checked off the list and forgotten.
That's a mistake that shows up years later.
Flood damage to HVAC equipment is insidious. Water doesn't just stop causing harm when it dries. It leaves behind salt, sediment, bacteria, and chemical residue that continue degrading your system's components long after the floodwaters are gone. And on the Texas Gulf Coast — where Hurricane Harvey, Tropical Storm Imelda, and regular flooding events have impacted thousands of homes — many systems running today are carrying hidden damage from water exposure that happened years ago.
If your home in Friendswood, Galveston, or the surrounding area has ever flooded, here's what you need to understand about the long-term effects on your HVAC system.
The Slow Damage You Can't See
Floodwater isn't clean water. Bayou and storm surge water carries a cocktail of sediment, organic matter, sewage, lawn chemicals, motor oil, and dissolved salts. When this water contacts your HVAC equipment — even briefly — it deposits contaminants that continue their work long after the water is gone.
Corroded Electrical Connections
This is the most dangerous long-term consequence. Floodwater leaves mineral deposits and corrosive residue on every electrical connection it touches: contactors, relays, capacitors, control boards, and wiring terminals. Initially, these connections may still function. But over months and years, the corrosion increases electrical resistance at each contact point.
Higher resistance means more heat generation at connections. You might notice your system's circuit breaker tripping occasionally, or the outdoor unit humming without starting. In worst cases, corroded connections arc — creating sparks at contact points that can melt wire insulation or ignite nearby materials.
Homes in Woodlawn in Friendswood experienced some of the worst flooding during Harvey, with water reaching 3-5 feet in many homes. Outdoor condensing units that sat submerged for days absorbed contaminants into every electrical junction. Even units that were professionally cleaned afterward may have residual corrosion in wire terminals and control boards that wasn't visible during initial assessment.
Contaminated Ductwork and Insulation
If floodwater reached your ductwork — which runs at or below floor level in slab-on-grade homes — the duct insulation absorbed contaminated water like a sponge. Flex duct insulation and duct board never fully dry in our humid climate. The moisture, combined with organic contaminants in the floodwater, creates a permanent mold habitat.
You might not smell it immediately. But as the mold colony grows and matures over months, you'll notice a musty odor when the system runs, worsening allergy symptoms, or visible dark spots at supply registers. By this point, the contamination has usually spread throughout the entire duct system.
Stevenson Park in Friendswood saw significant flooding during Harvey, and many of those homes have ground-level duct runs that were fully submerged. Homeowners who replaced drywall and flooring but left the ductwork in place may still be breathing air that passes through contaminated insulation every day.
Pro Tip: If your home flooded and you're experiencing any respiratory symptoms that improve when you leave the house, contaminated ductwork is one of the first things to investigate. A professional air quality test can determine whether mold levels in your indoor air are elevated compared to outdoor baseline levels.
Weakened Compressor Internals
The compressor is a hermetically sealed unit — but "sealed" has limits. If your outdoor unit sat in floodwater, especially for more than a few hours, there's a real possibility that contaminated water entered the compressor through the service valves, electrical terminal seals, or pressure relief ports.
Water inside a compressor causes several progressive failures:
- Acid formation. Water reacts with refrigerant oil to form hydrofluoric and hydrochloric acids. These acids slowly eat away at compressor bearings, valve plates, and motor windings.
- Bearing wear. Sediment in the oil acts as an abrasive, accelerating bearing wear. You might hear a gradually increasing grinding or rumbling noise from the outdoor unit.
- Winding insulation breakdown. Acid and moisture degrade the electrical insulation on the compressor motor windings. This eventually causes a short circuit that kills the compressor — often 2-5 years after the original flood event.
The timing is what catches people off guard. A compressor damaged by flooding may run for three, four, even five years before it fails — long after the homeowner has stopped thinking about the flood as a cause.
Air Handler Cabinet Degradation
The air handler (indoor unit) typically has a galvanized steel cabinet. Floodwater strips protective zinc coatings and deposits corrosive residue in seams and crevices. Over time, the cabinet corrodes from the inside out. You may see rust stains on the floor beneath the unit, or notice the cabinet developing soft spots or holes.
A corroded cabinet creates air leaks that reduce system efficiency and allow unfiltered, unconditioned air to enter the system. It also compromises the drain pan, potentially leading to water damage around the unit.
Galveston's Additional Challenges
Galveston faces a double threat: flood events are more frequent, and the floodwater often carries saltwater from storm surge. Salt dramatically accelerates every form of corrosion described above.
Neighborhoods like San Jacinto and Lasker Park have experienced repeated flooding events — not just Harvey, but regular heavy rain flooding and occasional tropical storm surge. The cumulative effect on HVAC systems in these areas is significant. Each flood event adds another layer of contamination, and salt deposits from storm surge are particularly destructive to electrical components and coil surfaces.
When to Call a Pro: If your home has flooded at any point — whether it was Harvey, a subsequent storm, or a plumbing failure — and your HVAC system hasn't been professionally assessed since, schedule a post-flood system inspection. The assessment checks every component for hidden damage and gives you a clear picture of your system's current condition and remaining useful life.
What a Post-Flood HVAC Assessment Checks
A thorough post-flood assessment goes far beyond a standard maintenance visit. Here's what a qualified technician evaluates:
Electrical system integrity:
- Amperage draw on all motors and the compressor (compared to nameplate ratings)
- Contact resistance at all accessible wiring terminals
- Capacitor health and rated vs. actual capacitance
- Control board condition, checking for corrosion or discoloration
- Contactor pitting and arc damage
Refrigerant system health:
- Operating pressures compared to manufacturer specifications
- Subcooling and superheat calculations to identify internal restrictions
- Acid test of refrigerant oil (indicates water contamination)
- Compressor amperage and temperature analysis
Ductwork condition:
- Visual inspection of accessible duct runs for mold, staining, or deterioration
- Air sampling at supply registers for mold spore counts
- Duct pressure testing to identify leaks from corroded joints
- Insulation condition assessment
Structural and cabinet integrity:
- Air handler cabinet corrosion assessment
- Drain pan condition and slope
- Outdoor unit cabinet, base pan, and mounting hardware
- Refrigerant line insulation condition
The Decision: Repair, Remediate, or Replace
After assessment, the findings typically lead to one of three paths:
Minor damage — targeted repairs. If corrosion is limited to accessible components like contactors, capacitors, and terminal blocks, replacement of those components and application of corrosion inhibitors may extend the system's useful life at reasonable cost.
Moderate damage — remediation. If ductwork is contaminated but the equipment is sound, duct cleaning or replacement combined with component repairs can restore the system. This is often the path for homes where only the ductwork was exposed to floodwater.
Significant damage — system replacement. If the compressor shows signs of internal contamination (high acid levels, abnormal amperage, unusual noise), replacement is typically the better investment. A damaged compressor will fail — the question is when, not if. Replacing proactively lets you choose the timing and equipment rather than dealing with an emergency failure during a July heat wave.
Don't Wait for Failure
The most expensive way to deal with flood-damaged HVAC equipment is to wait until it fails. Emergency replacements cost more, take longer, and leave you without cooling or heating during the wait. A proactive assessment gives you information and options.
Frequently Asked Questions
How long after a flood does HVAC damage appear?
Electrical connection issues and mold growth typically become apparent within 6-18 months. Compressor failure from water contamination usually occurs 2-5 years after the flood event. Cabinet corrosion progresses continuously but may not become critical for 3-7 years.
My HVAC system was above the flood line. Should I still get it checked?
If your outdoor unit was submerged at all — even partially — yes. Also check ductwork that runs at floor level in slab-on-grade homes. Floodwater often reaches ductwork even when the main equipment stayed dry. High humidity during and after flooding can also cause condensation-related issues in duct systems.
Can flood-damaged HVAC equipment be claimed on insurance?
If the original flood damage was covered by flood insurance, related HVAC damage discovered later may be claimable — but documentation is critical. A professional assessment report that links current equipment condition to the flood event strengthens any claim. Contact your insurance provider with assessment documentation rather than filing a claim based on assumptions.
Is it safe to run an HVAC system that was flooded?
It depends on the extent of exposure and what maintenance has been done since. A system with corroded electrical connections poses a genuine safety risk (fire and shock hazards). If you see scorch marks, smell burning, or notice the breaker tripping, stop using the system and get it inspected immediately.
Flood damage doesn't have an expiration date. If your Friendswood or Galveston home has experienced flooding — whether recently or years ago — understanding what's happening inside your HVAC system is the first step toward protecting your comfort, your safety, and your investment.
Need a post-flood HVAC assessment? Schedule a service call for expert system evaluation in Friendswood/Galveston.
