Indoor Air Quality – IAQ Blog
How Safe Is Your Indoor Air Quality?

Indoor Air Quality – IAQ
Indoor air quality (IAQ) has become one of the most important topics in the HVAC industry. In the past, the focus of HVAC design was simple comfort—primarily maintaining temperature. Today, we understand that temperature is only one piece of the comfort and safety equation.
According to research published by PubMed.gov, most illnesses linked to environmental exposure originate indoors. When you consider the cumulative time people spend at home, at work, and in other enclosed spaces, IAQ becomes a critical component of long-term health.

What Affects Indoor Air Quality?

Poor IAQ is more than just “stale air.” Buildings can accumulate a wide range of contaminants, including:

• Cleaning solvents
• Paints and chemicals
• Pesticides
• Carbon dioxide (CO₂)
• Volatile organic compounds (VOCs)
• Radon gas
• Off-gassing from furniture, carpet, and building materials
• Fumes from attached garages

These contaminants can contribute to:

• Eye, nose, or throat irritation
• Headaches
• Drowsiness or fatigue
• Allergic reactions
• Asthma triggers
• Reduced cognitive function
• Over the long term, even serious health risks

Simple Solutions You Can Start With
Basic maintenance and proactive habits can dramatically improve IAQ.

Replace air filters regularly
Dirty filters restrict airflow and recirculate contaminants.

Use air purifiers or room air cleaners
Especially helpful for allergy or asthma sufferers.

Consider UV germicidal lamps
UV-C technology helps neutralize airborne pathogens.

Maintain your HVAC system
Inspection and cleaning of ducts and equipment can reduce:

• Dust buildup
• Mold
• Potential carbon monoxide leakage (in gas furnace applications)

These steps are cost-effective and provide immediate benefits.

IAQ in the Context of COVID-19 and Other Infectious Aerosols

The COVID-19 pandemic highlighted the importance of indoor ventilation. Organizations like ASHRAE—the American Society of Heating, Refrigerating, and Air-Conditioning Engineers—provide standards and recommendations to improve IAQ during infectious disease concerns.

ASHRAE Standard 62 specifies minimum fresh air ventilation rates, ranging from 15 to 60 CFM per person, with most facilities falling within the 15–35 CFM per person range.

In April 2020, ASHRAE released their Position Document on Infectious Aerosols, noting:

“The risk of pathogen spread… can be affected both positively and negatively by the airflow patterns in a space and by HVAC and local exhaust systems.”
In other words, your HVAC system can either help mitigate pathogen spread—or worsen it—depending on design and operation.

The Role of Economizers

For commercial buildings, economizers provide a controlled method of introducing fresh outdoor air. During favorable conditions, they allow “free cooling” by using outdoor air instead of mechanical cooling.

ASHRAE guidance for infectious aerosol control recommends:

• Increasing outdoor air ventilation
• Disabling demand-control ventilation where outdoor air is needed
• Operating systems for extended hours

However, operating with 100% outdoor air is not always feasible. Most rooftop units are not sized to handle extreme heating or cooling loads when conditioning full outdoor air continuously. Running in this mode 24/7 can drive energy costs to astronomical levels.

A balanced approach is needed:

• Increase fresh air when possible
• Avoid overloading HVAC equipment
• Maintain control of temperature and humidity levels

Energy Recovery Ventilation (ERV) Considerations

Although MicroMetl no longer manufactures ERVs, understanding their role helps contractors and building operators make informed decisions.
ERVs can:

• Exhaust stale indoor air
• Recover heat or cooling energy from that air
• Reduce the load on rooftop units
• Improve humidity control

However, ERV systems must be evaluated carefully when infectious aerosol concerns are present.

Airstream cross-contamination—called Exhaust Air Transfer Rate (EATR)—can allow small amounts of exhaust air to recirculate into the supply air. Some ERV technologies allow up to 5–10% EATR under certain conditions, which is acceptable under ASHRAE 62.1 for general ventilation but may not be appropriate during health-related situations.

When addressing infectious aerosols, ASHRAE advises:

“Bypass energy recovery ventilation systems that leak potentially contaminated exhaust air back into the outdoor air supply.”

Bypassing an ERV can create its own challenges, especially if the rooftop unit was sized with the ERV’s energy recovery in mind. This reinforces the importance of proper design and ongoing evaluation—not simply replacing equipment at face value.

Control CO₂ Levels for Better IAQ

CO₂ levels are an effective indicator of ventilation adequacy in occupied spaces. Elevated CO₂ can cause:

• Drowsiness
• Reduced concentration
• Headaches
• Increased fatigue

Here are common CO₂ exposure ranges:

Demand-control ventilation strategies that rely on CO₂ sensors can help maintain safe levels, especially in:

• Classrooms
• Meeting rooms
• Gyms
• Auditoriums

Final Thoughts

Indoor Air Quality directly impacts comfort, health, and productivity. The keys to maintaining healthy IAQ include:

• Adequate ventilation
• Proper filtration
• Regular maintenance
• Monitoring CO₂ and VOC levels
• Using HVAC systems intelligently and efficiently

HVAC professionals should stay informed of evolving standards and educate building owners about the importance of IAQ and its direct effect on energy costs, health, and occupant comfort.