Plywood Air Handler platform vs. Aluminum Stand

Mold on HVAC plywood platform.



When setting up an HVAC system, choosing the right material for the return box is crucial. With the potential for overflowing drain lines in mind, this decision becomes even more vital. Overflowing drain lines can lead to mold growth, especially when wood return boxes are involved. In this article, we will explore the implications of this common issue and discuss how choosing the right materials can mitigate potential damage.


The Issue with Wood Return Boxes:

  • Overflowing Drain Lines:

It’s not uncommon for drain lines of an HVAC system to overflow. Factors such as blockages, incorrect installations, or even just regular wear and tear can cause this. When the drain line overflows, moisture can quickly come into contact with surrounding materials – including the HVAC return box.

  • Wood’s Susceptibility to Moisture:

Wood, being a porous material, readily absorbs moisture. Once wood becomes damp, it offers an ideal environment for mold and mildew to grow. In warm and humid conditions, such as those in many HVAC settings, mold can proliferate rapidly on wet wood.


Case in study:

A client contacted FSE LLC over concerns for mold growth in her HVAC unit.  She noted the drain line had overflowed multiple times and had never been dried out properly.


Upon inspection of the HVAC unit and wooden stand it was noted that there was signs of water intrusion and water damage along the stucco finished, plywood stand on which the HVAC unit sat.

Upon Further inspection of the under side of the HVAC unit shoes the plywood substructure discolored with visible microbial growth.

Lab analysis, in fact, did confirm the presence of mold along the plywood substructure.


Consequences of Mold Growth:


1. Health Concerns: Mold can produce allergens, irritants, and potentially toxic substances. Inhalation of or exposure to these can lead to respiratory problems, allergic reactions, and other health issues.

2. System Efficiency: Mold growth can restrict airflow, causing the HVAC system to work harder and thus reducing its efficiency and lifespan.

3. Aesthetic Issues: Mold manifests as unsightly black or green patches, causing aesthetic concerns and potentially decreasing the value of a property.

Why Aluminum Stands Might Be a Better Choice:

Given the susceptibility of wood to moisture and mold, many experts advocate for the use of non-porous materials like aluminum for HVAC return boxes.

Advantages of Aluminum:


1. Non-porous Nature: Aluminum does not absorb moisture like wood does, which reduces the chances of mold growth significantly.

2. Durability: Resistant to rust and corrosion, aluminum has a notably longer lifespan in humid conditions compared to wood.

3. Low Maintenance: Aluminum stands require minimal maintenance, especially when considering the mold issues wood can present.

In Conclusion:


Overflowing drain lines pose a significant threat to wood return boxes, primarily due to the risk of mold growth. Choosing non-porous materials like aluminum can reduce these risks, ensuring a healthier environment and a more efficient HVAC system. It’s crucial for homeowners and building managers to be aware of this issue and to make informed choices when installing or maintaining their HVAC systems.