Ducting located in crawlspaces is especially vulnerable to moisture, temperature fluctuations, and poor ventilation. When metal ductwork corrodes, its ability to distribute conditioned air efficiently is compromised, and it may introduce air quality issues into the living space above.
Why Crawlspace Ducting Corrodes
High Moisture Levels: Damp crawlspaces create condensation on cool duct surfaces, accelerating rust.
Inadequate Insulation: Uninsulated or poorly wrapped ducts sweat when warm air meets cooler crawlspace air.
Standing Water or Poor Drainage: Persistent moisture or flooding in the crawlspace increases corrosion risk.
Age of the Ducting: Over time, galvanized coatings wear away, leaving bare metal exposed to air and water.
Risks of Corroded Ducting
Reduced Energy Efficiency: Rust holes or gaps allow air leaks, forcing HVAC systems to work harder.
Indoor Air Quality Issues: Rust flakes, dust, or even mold spores can be drawn into the duct system.
Structural Concerns: Severely deteriorated ducts may collapse, restricting or cutting off airflow entirely.
Pest Intrusion: Openings in corroded ductwork can allow insects or rodents to enter and spread contaminants.
Recommended Actions
Inspection
Confirm whether corrosion is surface-level (cosmetic) or structural (holes, leaks).
Use a moisture meter to evaluate crawlspace humidity levels.
Moisture Control
Install or repair vapor barriers to limit ground moisture.
Improve drainage and ventilation, or consider encapsulating the crawlspace.
Repair or Replacement
Surface Rust: Wire-brush and seal ducts with a rust-inhibiting coating, followed by insulation wrap.
Severe Corrosion: Replace affected sections with new galvanized or insulated ducting.
Preventive Measures
Ensure ducts are sealed and insulated to minimize condensation.
Regularly monitor crawlspace conditions to prevent recurrence.
Conclusion
Corroded crawlspace ducting is a sign of ongoing moisture problems and may also reduce HVAC efficiency while contributing to poor indoor air quality. Addressing both the root cause (moisture control) and the ductwork condition is essential to restoring system performance and protecting the home.