What High Humidity Does to a Commercial Building and the People Inside It
High indoor humidity in a commercial building is not simply a comfort issue. It is a building health problem that damages the structure, accelerates HVAC equipment deterioration, and affects the well-being and productivity of everyone inside. In Indiana, where summer relative humidity regularly exceeds 65 percent and stays elevated through the night, commercial buildings face sustained moisture pressure throughout the cooling season. Mission Mechanical has managed commercial indoor environment issues across central Indiana for 23 years, holding Indiana License CP 10200022, maintaining a BBB A+ accredited rating, and consistently recognized on Google and Yelp for commercial HVAC and IAQ service quality. This article covers what high humidity actually does inside a commercial building, and what building owners and facility managers can do to address it.
The EPA estimates that indoor air can be two to five times more polluted than outdoor air. Humidity is a primary driver of that gap, because excess moisture supports the biological growth, equipment degradation, and material damage that worsen indoor conditions over time. Understanding the specific effects of high humidity on a commercial building provides the context for addressing it systematically rather than reactively.
What High Humidity Means in the Context of Commercial Buildings
Relative humidity measures the amount of water vapor in the air as a percentage of the maximum it could hold at that temperature. ASHRAE standards for commercial building thermal comfort and indoor air quality establish an acceptable indoor relative humidity range of 30 to 60 percent for occupied spaces. Relative humidity consistently above 60 percent inside an occupied commercial building creates conditions that support mold and bacterial growth, increase occupant discomfort, and begin to degrade building materials and mechanical systems.
In Indiana, outdoor relative humidity during the summer cooling season commonly ranges from 65 to over 80 percent. The commercial AC system is the primary line of defense against outdoor moisture infiltrating indoor spaces and against moisture generated by building occupants accumulating to problematic levels. A well-functioning, correctly sized AC system maintains indoor humidity within the acceptable range automatically. When the AC system is oversized, poorly maintained, or insufficient for the latent load of the building, indoor humidity climbs even when air temperature appears controlled.
What High Humidity Does to the Building Structure
Moisture Absorption in Building Materials
Wood framing, drywall, and flooring materials absorb airborne moisture when indoor humidity stays consistently above 60 percent. Wood swells, warps, and weakens as moisture content increases. Drywall becomes soft and begins to support mold growth. Wood flooring buckles and gaps change. These effects develop gradually over months and seasons, making them easy to attribute to other causes. By the time the damage is visually obvious, it has typically been developing for an extended period.
Mold Growth on Building Surfaces
Mold requires three conditions to grow: a surface, organic material, and moisture. Commercial buildings provide all three in abundance, and persistent humidity above 60 percent is the factor that activates growth where it would otherwise not occur. Mold appears first in areas with the highest moisture accumulation, including restrooms, storage rooms, areas near exterior walls, and within HVAC equipment itself. Once established, mold growth releases spores throughout the building, affecting air quality across all occupied zones.
Corrosion of Metal Building Components
Metal components, including HVAC ductwork, equipment supports, structural fasteners, and electrical enclosures, corrode more rapidly in high-humidity environments. Ductwork seams develop rust that compromises air sealing. Equipment support frames corrode at contact points. Rooftop HVAC curb assemblies experience accelerated deterioration. The timeline for corrosion-related material failures shortens when indoor humidity is persistently elevated above recommended levels.
What High Humidity Does to Commercial HVAC Equipment
HVAC equipment is designed to operate within the expected indoor environment of the building it serves. Sustained humidity above recommended levels affects every major component category. Evaporator coils support faster biological growth in humid conditions, affecting both air quality and heat transfer efficiency. Condensate drain pans and drain lines develop algae blockages more quickly. Electrical components, including contactors, control boards, and motor windings, deteriorate faster in humid environments. A commercial AC system operating in a consistently high-humidity building requires more frequent maintenance attention to maintain performance and longevity.
What High Humidity Does to the People Inside a Commercial Building
Thermal Comfort and Perceived Temperature
The human body cools itself through evaporation of perspiration. When ambient humidity is high, perspiration cannot evaporate efficiently, and the body’s cooling mechanism is impaired. The result is that people feel warmer than the measured air temperature when humidity is elevated. A commercial building held at 74 degrees Fahrenheit with 70 percent relative humidity will feel less comfortable than the same building at 74 degrees with 50 percent relative humidity. Occupants in high-humidity buildings frequently report discomfort even when thermostats read acceptable temperatures, creating chronic complaints that temperature adjustment alone cannot resolve.
Health and Productivity Effects
High indoor humidity supports the biological growth of mold, bacteria, and dust mites, all of which are known respiratory irritants and allergen sources. Research consistently links elevated indoor humidity to increased rates of respiratory symptoms, allergic reactions, and reported illness among building occupants. Beyond health effects, the discomfort associated with high humidity impairs concentration and performance. Studies on indoor environmental quality and worker productivity show measurable performance decrements in poorly controlled thermal and humidity environments compared to environments maintained within ASHRAE recommended ranges.
The Connection Between Commercial AC Performance and Humidity
Commercial AC systems remove humidity as a byproduct of cooling. When the evaporator coil cools the supply air below its dew point, moisture condenses on the coil and drains away. The quantity of moisture removed depends on how long the system runs, the temperature of the coil, and the airflow volume across it. A system that is correctly sized, properly maintained, and operating with clean coils and correct refrigerant charge removes significant moisture from the building air during each cooling cycle.
An oversized commercial AC system is the most common HVAC-related cause of persistent indoor humidity problems. An oversized system cools rapidly, reaches set temperature quickly, and shuts off before the coil has been in contact with building air long enough to remove adequate moisture. The building arrives at the correct temperature but carries high moisture content. This pattern, called short cycling from oversizing, produces a building that is cool but clammy. The solution is not a thermostat adjustment; it is either system right-sizing or supplemental dehumidification to address the latent load independently.
See our commercial indoor air quality services for assessments, dehumidification, and ventilation improvements for commercial properties in central Indiana. Commercial AC maintenance that keeps coils clean, drain pans clear, and refrigerant properly charged is also a foundational step in humidity management.
Solutions for Commercial Building Humidity Problems
- HVAC system sizing evaluation: If the AC system is oversized and short cycling, system right-sizing through replacement or the addition of dedicated dehumidification is the most effective long-term solution
- Dedicated commercial dehumidifiers: Standalone commercial dehumidification equipment addresses latent load independently of temperature, allowing the AC to run on temperature while the dehumidifier manages moisture
- Ventilation system review: Oversized fresh air intakes or improperly operating economizer dampers can introduce humid outdoor air at rates that exceed the dehumidification capacity of the AC system
- Pre-season AC maintenance: Clean coils, correct refrigerant charge, and clear drain lines are prerequisites for effective dehumidification through normal AC operation
- Energy recovery ventilation: ERV systems pre-condition incoming outdoor air, reducing the humidity load that ventilation introduces into the building
- Building envelope assessment: Moisture intrusion through the building envelope, including roof leaks, failed window seals, and foundation moisture, adds to indoor humidity loads that the HVAC system must overcome
Contact Mission Mechanical at 317-733-8686 or request service online to schedule an IAQ evaluation for your commercial property. We serve commercial buildings throughout the Indianapolis area, Fishers, Carmel, Noblesville, and communities across central Indiana.
Frequently Asked Questions
What is considered high humidity in a commercial building?
The acceptable indoor relative humidity range for occupied commercial buildings, as established by ASHRAE Standard 55 for thermal comfort and supported by ASHRAE Standard 62.1 for indoor air quality, is generally between 30 and 60 percent. Relative humidity consistently above 60 percent in an occupied commercial space creates conditions that support mold growth, increase occupant discomfort, and begin to affect building materials and HVAC equipment.
What are the most visible signs of high humidity in a commercial building?
Visible signs include condensation on windows and glass partitions, water stains on ceilings or walls particularly near exterior surfaces, musty odors that do not resolve with standard cleaning, visible mold growth on surfaces in humid areas including restrooms and storage rooms, warping of wood surfaces or flooring, and occupant complaints about the air feeling heavy or damp even when the thermostat reads an acceptable temperature.
How does high humidity affect the structural elements of a commercial building?
Sustained high humidity causes wood framing, trim, and substrates to absorb moisture, leading to swelling, warping, and long-term structural weakening. Drywall absorbs moisture and becomes a substrate for mold growth. Metal components including ductwork, fasteners, and equipment supports corrode more rapidly in high-humidity environments. Flooring adhesives can fail, and moisture accumulation in the building envelope can cause insulation to lose thermal performance.
What does high indoor humidity do to commercial HVAC equipment?
HVAC components exposed to sustained high humidity experience accelerated corrosion on heat exchanger surfaces, coil fins, and electrical connections. Drain pans and drain lines develop algae and mold growth more rapidly. Ductwork interior surfaces in humid environments support biological growth that affects air quality and duct integrity over time. Electrical components including contactors and control boards deteriorate more quickly in humid conditions.
How does humidity affect the people working in a commercial building?
High indoor humidity directly affects thermal comfort because the human body depends on evaporation of perspiration for cooling. When ambient humidity is high, sweat does not evaporate efficiently, causing people to feel hotter than the measured air temperature. High humidity also supports growth of biological contaminants including mold and dust mites that can cause or worsen respiratory symptoms. Research links poor indoor humidity control to increased employee discomfort, fatigue, and reduced concentration in occupied commercial spaces.
What is the relationship between commercial AC performance and indoor humidity control?
Commercial AC systems remove moisture from the air as a byproduct of cooling. When the evaporator coil cools the air below its dew point, moisture condenses on the coil and drains away. A well-functioning, correctly sized AC system maintains indoor humidity within the acceptable range during normal summer operation. A system that is oversized, poorly maintained, or running at part load removes insufficient moisture, allowing indoor humidity to climb even when temperature is controlled.
Why does Indiana present particular humidity challenges for commercial buildings?
Indiana falls within a humid continental climate zone. Summer relative humidity consistently exceeds 65 percent outdoors, with overnight humidity regularly above 80 percent. During warm, humid nights, building envelopes absorb outdoor moisture. On days when outdoor temperatures are mild but humidity is high, some building owners reduce or shut off AC, allowing humid outdoor air to infiltrate and accumulate inside. This pattern is particularly problematic in older commercial buildings with lower air sealing levels.
How does commercial AC oversizing cause indoor humidity problems?
An oversized commercial AC system cools the air rapidly and reaches the thermostat setpoint before it has run long enough to adequately dehumidify the building air. This short cycling provides temperature control but poor latent heat removal. The building feels cold and clammy because the air is cool but heavily loaded with moisture. The problem is most pronounced during mild weather when the cooling load is low and run times are short, which is also when outdoor humidity tends to be highest.
What ASHRAE standards apply to commercial building humidity control?
ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, establishes comfort parameters including acceptable humidity ranges. ASHRAE Standard 62.1, Ventilation and Acceptable Indoor Air Quality, addresses moisture as a factor in IAQ management. Both standards inform commercial building design and operation guidance regarding acceptable indoor humidity levels and the ventilation and mechanical conditioning approaches that support them.
Can mold grow in a commercial building even with air conditioning running?
Yes. Mold grows wherever moisture is present, regardless of air conditioning operation. Areas of the building that do not receive adequate conditioned airflow, spaces with persistent moisture sources (roof leaks, plumbing leaks), and areas where condensation forms on cold surfaces can develop mold growth even when the primary occupied spaces are cooled. Mold also grows readily on HVAC evaporator coils and in drain pans when maintenance is deferred.
What is the difference between sensible cooling and latent cooling in commercial HVAC?
Sensible cooling reduces air temperature. Latent cooling removes moisture from the air by condensing it on the evaporator coil. Both are components of the total cooling load. In Indiana summers, the latent load is high because of elevated outdoor humidity. A commercial AC system must handle both sensible and latent loads adequately to maintain comfortable indoor conditions. A system that handles sensible load but not latent load produces a building that is cool in temperature but uncomfortable due to high humidity.
How do high-humidity conditions in a commercial building relate to indoor air quality?
High indoor humidity directly supports the growth of biological contaminants. Mold, bacteria, and dust mites all thrive above 60 percent relative humidity. These biological pollutants are known triggers for respiratory symptoms and allergic reactions. The EPA ranks indoor air quality as a significant health concern, noting that indoor air can be two to five times more polluted than outdoor air. High humidity conditions consistently worsen the biological pollutant load in commercial buildings.
What types of commercial spaces are most vulnerable to high humidity problems?
Restaurants and commercial kitchens generate significant moisture through cooking and dishwashing. Server rooms and data centers produce heat that affects local humidity control. Medical facilities have strict environmental requirements including humidity ranges. Office buildings with high occupancy density and limited ventilation accumulate moisture from occupant respiration. Warehouses with large door openings and infrequent occupancy can develop stratified high-humidity zones. Each of these building types has specific humidity management considerations.
How can I tell if my commercial building has a humidity problem rather than a temperature problem?
Occupant complaints that describe the air as “heavy,” “stuffy,” or “clammy” often indicate humidity problems rather than temperature problems. If the thermostat reads an acceptable temperature but occupants are still uncomfortable, moisture content is frequently the cause. Condensation on cold surfaces, musty odors, and visible biological growth are confirming signs. An indoor relative humidity measurement above 60 percent on a regular basis confirms a humidity control problem.
What are supplemental dehumidification options for commercial buildings in Indiana?
For commercial buildings where the primary AC system cannot maintain acceptable humidity, dedicated commercial dehumidifiers can be installed to handle latent load independently of the cooling system. These units are sized for the building square footage and moisture load and operate when humidity exceeds setpoints regardless of whether the AC is also running. They are particularly useful for buildings with mild-weather humidity problems when the AC is not running frequently enough to control moisture.
How does ventilation affect commercial building humidity control?
Ventilation introduces outdoor air into the building. In Indiana summers, outdoor air is warm and humid. Ventilation during high-outdoor-humidity conditions can add significantly to the indoor moisture load. ASHRAE 62.1 requires minimum outdoor air delivery for acceptable indoor air quality, but the design of ventilation systems can include energy recovery ventilation that pre-conditions incoming outdoor air to reduce the humidity and temperature load it adds to the building.
Can a commercial building have low humidity in winter and high humidity in summer?
Yes, and this is the typical pattern for Indiana commercial buildings. Heating systems dry indoor air significantly in winter, often pushing humidity well below the acceptable range and causing occupant discomfort from dry air, static electricity, and respiratory irritation. In summer, the same building may struggle with excess moisture. Humidity control for commercial buildings in Indiana involves both humidification and dehumidification capabilities to maintain acceptable conditions year-round.
What should a facility manager do when a commercial building smells musty in summer?
Musty odors in a commercial building are a strong indicator of mold or biological growth, typically in HVAC equipment, ductwork, or building materials exposed to moisture. The source should be investigated professionally. HVAC coil and drain pan inspection is a logical first step because mold growth in the air handling system distributes spores throughout the building. If coil and drain conditions are acceptable, a broader building investigation for moisture intrusion sources is warranted.
Is condensation on commercial building windows a sign of a humidity problem?
Condensation on interior window surfaces indicates that the window surface temperature is at or below the dew point of the indoor air. This means the indoor air contains enough moisture that it is condensing on the coldest available surface. In summer, this can occur on windows with high solar exposure if the AC is overcooling near the glass. In transition seasons, condensation near windows often indicates high indoor humidity from inadequate dehumidification.
How does an improperly sized fresh air intake contribute to humidity problems in commercial buildings?
An oversized fresh air intake introduces more humid outdoor air than the AC system can dehumidify under certain conditions, particularly during mild weather when the cooling system is not running at full capacity. Fresh air intake sizing should be matched to both the ventilation requirement per ASHRAE 62.1 and the dehumidification capacity of the HVAC system serving the zone.
What is a humidistat and should commercial buildings use one?
A humidistat measures indoor relative humidity and can control equipment, ventilation dampers, or supplemental dehumidifiers based on humidity level rather than temperature alone. Commercial buildings with persistent humidity problems often benefit from humidistat-based control that activates dehumidification independently of temperature calls. Integrating humidity sensing into a building automation system provides more complete indoor environmental control.
Can commercial building insulation problems cause humidity issues?
Yes. Gaps in building envelope insulation allow warm, humid outdoor air to infiltrate and condense on cooler interior surfaces during summer. Missing or displaced insulation in roof assemblies can allow moisture to accumulate in the building structure. Thermal bridging at structural members creates cold spots where condensation forms. A building envelope assessment is warranted when persistent moisture problems cannot be fully resolved through HVAC measures.
How often should commercial HVAC drain pans be cleaned in high-humidity climates like Indiana?
In Indiana summer conditions, commercial HVAC drain pans should be inspected at minimum during spring pre-season service and again at mid-season if the building has a history of biological growth in the drain system. High-moisture environments and systems with persistent algae growth may require more frequent attention. Drain pan tablets that inhibit algae growth are a useful addition during the operating season.
What is the dew point and how is it relevant to commercial building humidity management?
The dew point is the temperature at which moisture in the air begins to condense. When a surface in a building is colder than the dew point of the indoor air, condensation forms on that surface. Managing indoor humidity levels (which directly affects dew point) reduces the conditions under which condensation forms on building surfaces and HVAC equipment. Monitoring dew point in addition to relative humidity gives a more complete picture of indoor moisture conditions.
Can UV light systems in commercial HVAC help with humidity-related mold problems?
UV light systems installed in commercial HVAC equipment, particularly near evaporator coils, reduce biological growth on coil surfaces and in the air stream. They address the biological consequences of moisture accumulation rather than the moisture itself. UV systems are a useful component of commercial IAQ management in humid climates but are most effective when paired with adequate dehumidification that reduces moisture levels rather than treating only the symptoms.
How should a commercial building manager approach diagnosing a persistent humidity problem?
Start with measuring actual indoor relative humidity at multiple locations and times of day, including both occupied and mechanical areas. Review AC operation for run time adequacy (systems that short cycle may not dehumidify effectively). Inspect HVAC coils and drain pans for biological growth. Check for moisture intrusion through the building envelope. Review ventilation system damper operation and outdoor air delivery volume. A Mission Mechanical IAQ assessment covers the HVAC-related elements of this investigation.
Does commercial building age affect humidity management?
Older commercial buildings often have less effective air sealing, older single-pane windows with more condensation risk, and HVAC systems not originally designed to handle the combination of ventilation and dehumidification required by current standards. Newer buildings with better envelope performance may have different humidity challenges related to very tight construction and insufficient ventilation. Both scenarios are addressable but require different approaches.
What is the long-term financial impact of unmanaged humidity problems in a commercial building?
Sustained high humidity causes cumulative damage to building materials, HVAC equipment, and building contents. Mold remediation in commercial buildings can be expensive and disruptive. Premature replacement of HVAC equipment due to corrosion-accelerated deterioration adds to capital expenditure. Tenant complaints, lease violations related to building conditions, and potential health-related liability all create financial exposure. Proactive humidity management is substantially less expensive than addressing the damage from uncontrolled moisture.
Where can I get a commercial indoor air quality and humidity assessment in Indiana?
Mission Mechanical provides commercial indoor air quality assessments for buildings throughout central Indiana, evaluating HVAC system performance, ventilation adequacy, and humidity control as part of a comprehensive IAQ evaluation. Contact us at 317-733-8686 or request service online. See our commercial indoor air quality services for the full scope of IAQ solutions we provide.
When to Bring in a Commercial IAQ Professional
When occupant complaints, visible moisture damage, or persistent musty odors indicate a humidity problem, an HVAC and IAQ assessment from a qualified contractor can identify whether the issue originates in HVAC performance, equipment sizing, ventilation design, or the building envelope. Mission Mechanical performs commercial IAQ assessments that evaluate the HVAC system’s humidity control performance, ventilation configuration, and equipment condition to identify practical improvements.
Commercial indoor air quality and humidity solutions in central Indiana. Mission Mechanical is Indiana licensed, NATE certified, BBB A+. Call 317-733-8686 or request service online.
