Can Putting Insulation on My Heater Ducts Cause Mold & Mildew?

Mold and Ducts

• Most duct work consists of thin sheets of metal. If moisture accumulates in the ducts, combined with organic materials like soil, mold and mildew can begin to grow. This typically happens if the duct work suffers from some sort of leak, or if extremely dirty filters push dirt and dust through the system, but seldom happens in a well-managed HVAC system. Adding insulation to the ducts does not increase this mold risk.

Heating Duct Insulation

• Heating duct insulation is primarily an energy-saving material. Since less air is lost through the ducts, the system heats and cools more effectively with less energy use. Heating duct insulation wraps directly around the ducts like foil or bubble wrap, except most duct insulation products consist of fiberglass or foam. Foam is mold resistant because it does not hold water, and fiberglass (though more absorbent) contains no organic materials, so the insulation products themselves will not contribute to mold growth.

Moisture Concerns

• Since heating duct insulation prevents the loss of air from the ducts, naturally it also prevents the loss of moisture. Since the accumulation of moisture can contribute to mold growth, this raises some concerns. If air flows through the heating ducts with greater effectiveness, moisture also evaporates more readily, so once again, moisture should not become a persistent problem, unless a more serious problem exists within the system.

Finding Mold

• Heating duct insulation can improve the effectiveness of your heating and cooling system without increasing your mold risk. But if you begin to notice the musty smell of mold inside your vents, or if you suffer mold-related systems, like difficulty breathing or respiratory infection with no visible cause, call an HVAC or mold remediation expert to examine the system for leaks. The problem may result from something as simple as a cooling coil, or the unit may have serious damage.