A musty odor in a commercial building is more than an inconvenience. It can be a warning sign that moisture, accumulated debris or microbial contamination is present somewhere in the building or HVAC system. Air fresheners, fragrances and odor-masking products may temporarily change what occupants smell, but they do not identify or correct the condition producing the odor.
For facility managers, the most effective response is to investigate the source. Cooling coils, condensate drain pans, wet insulation, porous duct liners, water-damaged building materials and other moisture-affected surfaces can all contribute to recurring odor complaints. EPA guidance emphasizes that moisture control is fundamental to preventing mold and other biological growth in buildings and HVAC systems.
A Musty Smell Is a Clue, Not a Diagnosis
Musty odors are commonly associated with damp conditions and microbial growth, but odor alone cannot tell a facility manager exactly what is happening or where the source is located.
An odor investigation should consider both the occupied space and the HVAC system. EPA guidance for commercial buildings identifies pollutant and odor sources, HVAC design and maintenance, moisture and humidity, ventilation and occupant conditions as interacting factors in indoor air quality.
The goal should be source identification. If an odor disappears after an air freshener is used but returns when the HVAC system starts, after a humid weekend or following a period of building shutdown, those patterns can provide useful clues.
Start With Moisture
Persistent musty odors should trigger a search for moisture. Roof and plumbing leaks, condensation, high indoor humidity, wet ceiling materials, damp insulation, standing water and poorly draining HVAC components can all create conditions that support microbial growth.
EPA states that controlling moisture is the most effective way to prevent biological growth in air ducts. If moisture is not corrected, cleaning alone may provide only temporary improvement because the conditions that allowed contamination to develop remain in place.
Cooling Coils Are Designed to Get Wet
A commercial cooling coil removes heat and moisture from the airstream. As warm air passes across the cold coil, water condenses on the coil surface and should flow into a drain pan.
This normal process makes coil cleanliness and drainage especially important. Dust and debris can accumulate on the coil, while moisture is present whenever the system is dehumidifying. NADCA notes that evaporator coils can become locations for particulate, bacteria and suspected microbial growth when contamination and moisture are present.
A dirty or contaminated coil can therefore be both a maintenance concern and a possible contributor to odor complaints.
Drain Pans Can Become Odor Sources
Condensate pans are intended to collect water from the cooling coil and drain it away. They should not become reservoirs of stagnant water, sediment and debris.
EPA guidance warns that standing water in improperly designed or maintained drain pans can create a microbial habitat. Drain pans, condensate lines and traps should be inspected for cleanliness and proper drainage as part of an investigation into recurring musty odors.
Dry drain traps can create a different odor problem. During periods when condensate formation is low, a trap can dry out and allow sewer or drainage-system gases to be drawn into an HVAC unit and distributed through the building.
What Is Happening Downstream of the Coil?
Moisture does not always remain where it is supposed to. Condensate carryover, high humidity, air leakage, inadequate insulation or other conditions can allow moisture to reach duct surfaces downstream from cooling equipment.
EPA recommends close attention to ductwork immediately downstream of cooling and dehumidification coils because these areas can be vulnerable to moisture and dirt accumulation. When dust and moisture remain together, conditions can support mold growth on HVAC surfaces.
If musty odors appear primarily when an air handler operates, inspecting the coil section and downstream ductwork can be an important part of tracing the source.
Porous Materials Require Special Attention
Porous materials behave differently from bare sheet metal. Fiberglass duct liner and other insulation products can provide valuable thermal and acoustic performance, but if they become wet they can retain moisture within their structure.
EPA guidance states that wet or moldy fiberglass duct insulation cannot be effectively cleaned in the same manner as nonporous metal and recommends removal and replacement when the material is wet or visibly moldy.
NADCA’s commercial guidance similarly recommends that porous materials with mold growth be properly removed and replaced, followed by cleaning of the exposed surfaces.
Duct Liners Can Hide Problems From View
Internally lined ductwork may be difficult to inspect from occupied spaces. A supply register can look clean while moisture or contamination exists farther inside the system.
EPA notes that duct liner can trap and retain moisture when it becomes wet. Dirt and dust already present on surfaces can then provide material that supports microbial growth. Access and inspection are therefore important when odors persist without an obvious source in the room.
Facility managers should also look for deteriorated, damaged or delaminating liner rather than assuming every odor problem can be solved by surface cleaning.
Microbial Contamination Requires Source Control
When suspected microbial growth is identified, the first question should be why the material was able to grow. Water intrusion, condensation, poor drainage, uncontrolled humidity or another moisture source may be involved.
NADCA’s commercial guidance recommends further assessment when suspect mold or other biological activity is identified and calls for the cause and extent to be evaluated as appropriate. It also recommends inspecting supply and return ducts when suspect mold contamination is found in air-handling components.
Removing contamination without correcting the moisture source can set the stage for recurrence.
Why Odor-Masking Products Are Not the Solution
Fragrances and deodorizing products may temporarily overwhelm an unpleasant smell, but masking an odor is not source removal. It can also make it more difficult to determine whether the original odor is still present.
For HVAC systems, professional cleaning is based on physically removing accumulated contamination from affected components. NADCA’s commercial standard emphasizes mechanical cleaning and source removal, with surface treatments considered only after appropriate cleaning and cleanliness verification.
If a facility has a recurring musty odor, the priority should be to identify moisture, contamination or damaged materials rather than simply introducing another odor into the airstream.
Do Not Assume Every Musty Odor Is Coming From the Ductwork
HVAC systems are important to investigate, but commercial buildings contain many other possible odor sources. Wet carpet, ceiling tile, wallboard, pipe insulation, janitorial areas, plumbing systems, roof leaks, foundation moisture and stored materials can all contribute.
An effective investigation follows the odor and the moisture. Complaint history, building walkthroughs, HVAC inspection and moisture evaluation can help determine whether the source is localized to a room, associated with a particular air-handling system or coming from another part of the building.
When HVAC Cleaning Becomes Part of the Solution
If inspection identifies significant contamination within appropriate HVAC components, professional cleaning may be part of the corrective plan. Depending on actual conditions, the scope can include air-handling units, cooling coils, drain pans, fans, accessible ductwork, registers, grilles and other airside surfaces.
NADCA’s commercial guidance recommends wet cleaning coils, fans, condensate pans, drains and similar nonporous air-handling surfaces in conjunction with appropriate mechanical methods when conditions warrant.
The cleaning scope should be based on inspection rather than assumption, and any moisture source contributing to the problem should be corrected.
Fix the Source, Then Verify the Result
A successful odor investigation should end with more than a cleaner-smelling room. After corrective work, facility teams should verify that leaks have been repaired, condensate drains correctly, wet materials have been addressed, HVAC components are clean where required and the original odor complaint has improved.
Recurring odors after cleaning are a signal to continue investigating. There may be an unresolved moisture condition, a contaminated porous material or a source outside the HVAC system that still needs attention.
Musty Odors Should Not Become Part of the Building
Facility teams sometimes become accustomed to an odor that has been present for months or years. Occupants may describe it as the way a particular hallway, classroom, office or mechanical area has always smelled. But persistent musty odors deserve investigation.
Finding the source can uncover moisture, drainage, HVAC cleanliness or material conditions that are better addressed before they become larger maintenance and indoor air quality concerns.
Commercial HVAC Inspection and Cleaning From Advanced Air Duct Cleaning
Advanced Furnace and Air Duct Cleaning Inc. has served commercial, institutional and healthcare customers since 1964. Our experienced team provides professional air duct, air-handler, coil and HVAC system cleaning throughout New Jersey, Northern Delaware, Eastern Pennsylvania and Staten Island.
When a facility is experiencing recurring musty odors, Advanced can work with facility teams to inspect accessible HVAC components, identify areas of buildup within the cleaning scope and develop an appropriate professional cleaning plan.
Does your commercial building have a musty odor that keeps coming back? Contact Advanced Air Duct Cleaning to discuss an HVAC system inspection and professional cleaning plan that addresses the source instead of simply covering up the smell.