HVAC Systems and Mold: Air Handler and Ductwork Cleaning and Maintenance

Cesar Collado
March 23, 2020

Reading Time: 6 minutes

HVAC Systems and Mold: Air Handler and Ductwork Cleaning and Maintenance

The HVAC system is the most important investment made in any new or existing home.  Because of the expense, many homes have improperly fitted HVAC systems.  This error can be the cause of mold growth or it may spread mold throughout the home.  HVAC systems and ductwork design should be meticulously selected for each home. It requires careful calculations to determine the right size of the unit and ductwork designed for a particular floorplan, ceiling height, window number, sun exposure, etc.  Too large of a unit can cause condensation due to improper cycling.  Too small of a unit can lead to energy inefficiency and temperature discomfort.  In some cases, homeowners are given the options to add on “whole house” dehumidification, high efficiency filtration, etc. Read on to learn more about HVAC Systems and Mold. 

HVAC technicians that were interviewed estimate that a majority of homes have improperly sized HVAC systems.  This is frequently due to developers purchasing HVAC units in bulk for neighborhoods with homes that face different directions, have differing floorplans, and varied window exposure.  Often, the only criteria used in determining if an HVAC system was properly installed is whether or not it is able to maintain the desired temperature. Very little attention is given to whether all duct joints were properly sealed, whether the unit cycles as designed, proper filtration, or long-term maintenance protocols.

HVAC Systems and Mold

When a home develops an isolated mold problem, DIY cleaning and remediation will most often remedy the problem, provided the moisture source is identified and fixed in a timely manner.  If the moldy area is confined space smaller than a 3’x3’ (based on EPA recommendations –, DIY mold remediation can be done by homeowners as long as proper safety precautions are taken to avoid the spreading of mold spores into the air, the HVAC system, and other rooms.  One of the most important steps in remediation is to seal off the area being remediated.  This is because disrupting the mold can send numerous millions of spores into the air. (FYI, a single square inch of surface can hold over 1,000,000 spores.)  Any disruption will release spores into the air. If these spores make their way into the return air ducting of your HVAC system, your entire home can be contaminated.  When the mold issue is larger than that, or you are sensitive to mold yourself, it is best to hire a professional to remediate the problem with proper safety precautions.

Remediation professionals will not necessarily have the HVAC and ductwork cleaned if the work is properly sealed.

HVAC and Ductwork Cleaning

If the issue is bigger than one you can remedy easily, and/or mold is disrupted or has contaminated a home for a lengthy period of time, HVAC cleaning must be considered.  The HVAC system can be thought of as the “Lungs” of your home, intended to distribute comfortable and clean air throughout the home.

HVAC system cleaning should be considered in the following situations:

  • When mold contaminates building materials and removal or demolition is required to address damp, decayed, or moldy materials. The disruption of mold spores is inevitable and can fill the air, contaminate furnishings, and enter the home’s ventilation system.
  • A moldy or musty smell can be detected in adjacent rooms or directly from air registers.
  • When any major leak or flooding occurs that allows building materials or furnishings, such as drywall or carpeting, to fully absorb dampness.
  • When the moisture source occurs within the HVAC system, such as when condensation develops on the coils. Normal everyday dust or insulation combined with moisture can allow mold to grow and spread throughout the system and into the home ventilation, causing a systemic mold problem in the home.

HVAC Systems and Mold

  • When replacing HVAC filters and there is evidence of water condensation and mold.
  • When you or someone in the home is chronically ill, mold sensitive, immunocompromised, or subject to respiratory illness.

Additionally, children with developing lungs and compromised elderly may benefit greatly from the proactive cleaning of the HVAC system.

The potential for HVAC contamination is high. It is best to have an HVAC professional inspect and test the system.  Proper safety precautions, removal of the outside casing, and disinfecting specific areas may be required for correct cleaning. The cost to remediate or clean the HVAC unit, including the inside case and coils, ranges from $200-300 per system when performed by an HVAC professional. The cost to clean air duct systems ranges from $250-500 per home.

A thorough cleaning of the HVAC system after remediation may be necessary to ensure you are preventing the spread of mold throughout the house via ventilation. Heating and air conditioning ventilation can fairly evenly distribute mold spores throughout an entire home.

Fogging the Entire Home for Mold Maintenance Will Flush Your HVAC System if Done Properly

Whether you are fogging to maintain minimal fungal air counts, or fogging following repairs and remediation to reach all exposed surfaces in your home, there is a benefit of flushing the HVAC system with a botanical, antimicrobial fog.   Either the Bio-Balance Fog Kit or the Bio-Balance Deluxe Fogging Package can be used for this purpose.  The thick fog will force its way through the ductwork and the HVAC components.

Before fogging, remove and be prepared to replace the HVAC filter.  Turn the HVAC fan to the “On” position (rather than “Auto”).  Fog the home with a thick fog per the included instructions, making sure to point the fog machine toward the return air vent during the process. The HVAC fan will circulate the fog through the system and ductwork. Then turn the HVAC system off and the fan back to “Auto” for 24 hours to allow the fog to settle on the interior surfaces of the HVAC system and ductwork. After the fog dissipates and you feel safe to enter the home, replace the air filter with at least a MERV 11 rated filter and turn your HVAC system back on.  The HVAC system will recirculate the fog through the ductwork and air handler to treat mold spores and debris.  Wiping the registers with Bio-Balance Maintenance Solution or CitriSafe Mold Solution Concentrate is recommended. A thorough HEPA vacuuming and wiping down of all horizontal surfaces in the home with a microfiber towels is recommended to remove mold debris. If dust is visible, wet wipe with a microfiber cloth and Bio-Balance Maintenance Solution. “Cleaning dust is essentially cleaning mold.”

Fogging the HVAC System Only

If your home has been recently remediated and you have done periodic testing to ensure you do not have a mold problem, a more direct method of fogging the HVAC system can be done prophylactically.  By flushing the HVAC system with a botanical antimicrobial through the air intake vents, you can distribute the fog through the ductwork throughout the home.

Here are some steps to follow to identify the return vent(s).

  • The air return vent(s) are typically the largestvent(s) in your home.
  • Thevent(s) will not typically have louvers or slats behind the “grill”.
  • There may be an air filter connected to thisvent.
  • Turn the system fan on; if you hold a piece of paper or tissue in front of the vent, the paper/tissue should be pulled towards thevent.

Once the air return vent(s) have been identified, turn off the HVAC fan and carefully remove all air filters, placing them directly into a garbage bag (to prevent contaminating your home). Place the fogger inside the return vent(s) or focus fog production into the return vent(s).  Let the fogger flush your system for approximately 30 minutes (Your home will become foggy.). Keep the fan off for 24 hours before replacing the filter and turning the HVAC system back on.  During the treatment you will see the fog exit the air vents in your home.  The fog is safe to inhale; however, you can elect to stay out of the home for 8-24 hours until the fog dissipates.

HVAC Systems and Mold

This process will treat mold spores in the air and on the surfaces inside the HVAC unit and ductwork.  This does not replace a proper HVAC cleaning and disinfection if you have a significant mold problem.  The treatment will provide some piece of mind by reducing the fungal count in distributed air following a DIY remediation.