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By Nathan Gauthier

It has been about a century since the “I opened the window and in-flew-Enza” nursery rhyme first cautioned people against introducing too much fresh air into buildings. With the advent of air conditioning and mechanical ventilation, buildings in the US moved away from natural ventilation and as utility costs rose, there was a corresponding effort by designers and building operators to reduce outdoor air rates.

Most commercial buildings relied on heating, ventilation and air conditioning (HVAC) systems that recirculated return air with small amounts of fresh air added as needed to avoid acute impacts. Regardless of the original design intent, occupant densities tended to increase over time and outside air dampers were often closed by operations staff to save energy or address cold calls, and indoor CO2 levels rose well above ambient conditions. Much of the existing building stock was built and/or is being operated in this fashion, and everybody can relate to the experience of suddenly becoming sleepy in a crowded conference room as CO2 levels rise and fresh air is inadequate.

Today, indoor air quality experts and building design professionals alike agree some level of natural or mechanical ventilation is critical to human health and building durability.

ASHRAE 62.1 Ventilation for Acceptable Indoor Air Quality identifies outside air rates based on space type and is the industry standard. Designers typically size equipment to meet the ASHRAE standards, and owners and operators believe they’re acting responsibly if they can maintain these levels of outside air.

HVAC systems represent over 8% of total project cost for new schools and 16% of the building construction costs (MSBA). HVAC systems are responsible for more than 50% of annual energy consumption in educational buildings representing thousands of dollars in annual utility costs (CBECS 2012). Projects want to provide enough ventilation to avoid occupant health or building durability issues, while minimizing first costs and ongoing energy costs.

ASHRAE 62.1 is meant, however, to specify “minimum ventilation rates and other measures intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects” (ASHRAE 62.1-2010). It has changed over time and attempts to balance energy conservation with protecting human health, but at its core it tries to avoid acute health impacts such as the conference room full of yawning people. It assumes occupants need only as much outside air as it takes to avoid being visibly impacted by the lack of fresh air and designers typically size equipment accordingly.

Yet, there is a growing body of research that demonstrates human health and productivity benefits from “beyond code” ventilation. Green building rating programs reward projects for providing increased levels of fresh air beyond code (LEED v4, WELL v2).

Building occupants indicate a desire for fresh air and ventilation control, and complaints about poor indoor air quality when ventilation is inadequate consistently rank amongst the top to facilities managers (IFMA 2003).

There is no doubt that providing increased levels of outside air can be beneficial to occupants, yet it is still the norm to default to the ASHRAE minimum. 

Building owners that are aware of the significant health and productivity benefits of increased ventilation may want to request higher levels of outside air and smart HVAC design can greatly minimize the energy impacts of doing so.

Better Thinking, Productivity, Health and ROI

A study whose main author was from Harvard T. H. Chan School of Public Health “found an eight percentile increase in decision-making performance when ventilation was increased from 20 cfm/person to 40 cfm/person” and by inference, greater productivity (Ref 1).

Doubling the rate of ventilation boosted cognitive ability from the 62nd to 70th percentile with the biggest gains in “basic activity, information usage, breadth of approach, strategy and crisis response.”

The report cited other benefits of greater ventilation, including lower sick leave due to illness, flu and pneumonia, resulting in savings that “dwarf energy costs by a factor of six.”

The study looked at the energy impacts of changing ventilation rates and showed doubling ventilation rates from 20 cfm/person to 40 cfm/person costs only $14-$40 per year/person compared to an estimated productivity gain of up to $6500 per year/person.

Get more tips for Making the Business Case for Healthy Facilities in our recent podcast.

The report factored time spent indoors, worker salaries and benefits, the cost of operating buildings, and savings from a more productive workforce; and qualified the conclusion as a “conservative estimate of productivity gains and economic costs.”

The study concluded: “The public health benefits of enhanced ventilation far exceed the per occupant economic costs in U.S. cities. Even with conservative estimates, the increased productivity of an employee is over 150 times greater than the resulting energy costs.”

Using these numbers, it is difficult to make a defendable financial argument for choosing to design around the ASHRAE minimums.

Carbon Dioxide: More Than a Proxy

Carbon dioxide, a byproduct of exhalation, has been viewed as a surrogate or proxy for indoor air contamination; the more CO2 indoors, the worse the ventilation, and greater the buildup of airborne pollutants that may be harmful to people and productivity.

Now, CO2 itself is considered a contaminant in its own right. Another cognitive study found “on average, a 400 ppm increase in CO2 was associated with a 21% decrease [in cognitive scores]” (Ref 2).

Lawrence Berkeley Labs (LBL) found “moderately high indoor concentrations of carbon dioxide (CO2) can significantly impair people’s decision-making performance, with “particular implications for schools and other spaces with high occupant density” (Ref 3).

LBL assessed CO2 exposure at three concentrations: 600, 1,000 and 2,500 ppm using 24 subjects, mainly college students, for 2.5 hours at each of the three CO2 levels.

The best cognitive scores occurred at 600ppm CO2, and as LBL noted “in classrooms, concentrations frequently exceed 1,000 ppm and occasionally exceed 3,000 ppm.”

Chart: Courtesy of Lawrence Berkeley Labs

The evidence is clear, increasing ventilation is a proven strategy to increase productivity and enhance health.


1.   Economic, Environmental and Health Implications of Enhanced Ventilation in Office Buildings, 2015, International Journal of Environmental Research and Public Health.

2.   Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments, 2015, Environmental Health Perspectives.

3.   Elevated Indoor Carbon Dioxide Impairs Decision-Making Performance, 2012, Lawrence Berkeley Labs (LBL).

Author: Nathan Gauthier is Director of Facilities Management Integration and Sustainability with Shawmut Design and Construction, and serves on the Advisories of the Healthy Facilities Institute and the Indoor Wellness Council. Nathan teaches graduate courses on green building and occupant wellness at the Harvard Extension School. He has consulted on green building projects across 5 continents, more than 100 of which have become LEED certified (14 Platinum). Nathan chaired the USGBC Energy and Atmosphere Technical Advisory Group during development of LEED v4 and been a member of their board of directors at the state (MA) and national level. Nathan is a Licensed Residential Builder (MI), Certified Energy Manager, Facilities Manager, Energy Auditor, Construction Document Technologist, Ground Source Heat Pump Installer, Cx Process Provider, Existing Building Cx Professional, LEED AP, Fitwel Ambassador, NCI Charrette System accredited, and more. Nathan was selected as a 2014 LEED Fellow.

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