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Enhancing Health with Indoor Air

Compiled by Brian Gilligan, PE, GSA's Office of Federal High-Performance Buildings, and the Wellbuilt for Wellbeing Project Team
Why is indoor air important?

Americans spend 90% of their time indoors, so the quality of our indoor air is critical to our health, comfort and performance. Building systems help keep indoor air clean so that we do not get sick from exposure to toxins but more than that should help us stay well, energized, and productive. Recent studies suggest that improving indoor air quality beyond what conventional design requires could reduce rates of absenteeism, inflammation, infection and other symptoms of sick building syndrome by over a third and improve cognitive performance by as much as half. Perhaps there is an opportunity to help people feel healthier and perform better for having been in our buildings.

How might we improve Indoor Air?

There are four key levers to enhance human health, comfort, and performance by improving indoor air. Click each lever below to see specific actions and measurable environmental outcomes.

Lever 1: Provide More Fresh Air Lever 2: Remove Pollutants Lever 3: Manage Thermal Conditions Lever 4: Eliminate Indoor Sources

Building design is an evolving field but it is not always clear where it is best to go beyond convention as there is a balance to be found between the energy associated with heating, cooling and ventilating a space, and the ways in which doing so can elevate the human experience. Evidence-based practice can offer guidance and provide justification for doing so. Current standards for the indoor environment were developed by OSHA and ASHRAE, and they are convention for good reason. They are widely understood and reliably provide safe environments with a predictable level of occupant satisfaction.  However, design teams increasingly recognize opportunities not just to protect occupants from acute threats, but also to take an intentional approach to creating superior workplaces. One can see layers of tools and approaches that build on the conventional approach of protecting workers from acute risks and promoting thermal comfort and avoiding occupant complaints. These tools and approaches began with recognizing leadership relative to prevailing codes and standards and have expanded more and more to establishing stringent, research-based standards focused on occupant health and well-being.  All of these tools recognize the value of the “Four Levers” in improving workplace health, comfort, and performance.

Lever 1 - Provide More Fresh Air and Deliver it to the Breathing Zone

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Ventilation systems supply filtered outdoor air to keep indoor air clean and odor-free. They prevent the pollutants that people and their work bring with them from accumulating to unpleasant or unhealthy levels. Building systems are mostly designed to bring in a set minimum amount of outdoor air. Minimum outdoor air rates are most often set by ASHRAE Standard 62non government site opens in new window. The Standard considers the size of a building, its intended use, and the number of people expected to be in it. For office spaces it was developed from survey feedback regarding odors or complaints about the “bioeffluents” emitted by people. Under this “conventional” system, an office with 200 square feet for each person requires at least 17 cubic feet of outdoor air per minute per person (CFM/Person).

After the pandemic, ASHRAE released its Standard 241 for Control of Infectious Aerosols. It defines an increased “Equivalent Clean Air flow” during times of greater risk of infection. It is a flexible approach that allows building operators to meet increased requirements by providing a mix of more outdoor air, more recirculated indoor air cleaned with filtration or air cleaning technologies in the ventilation system, use of air cleaning technologies in individual spaces, and reduced occupancy. Under the standard, when agency or public health officials deem necessary, the amount of equivalent clean air in office spaces would be increased to 30 CFM/Person.

How much filtered outdoor air do existing systems suggest?

The table below identifies ventilation approaches ranging from conventional to more stringent levels.

Standards/Systems Minimum Ventilation Rate (@200SF/Person) CO2 Steady State*
ASHRAE 62.1non government site opens in new window, OSHA
~17 CFM/Person
ASHRAE 62.1: 5 CFM/Person + 0.06 CFM/SF
Demand Control Ventilation not required
1000 ppm
Enhanced (Better):
LEED v4non government site opens in new window / Well v2non government site opens in new window, Finnish SIAQ “Good”, Hong Kong “Excellent”
~22 CFM/Person
Demand Control Ventilation required if <40SF/Person
850 ppm
~27 CFM/Person
WELL (extra point): ASHRAE + 60%
Demand Control Ventilation required if <40SF/Person
750 ppm
Stringent (Best):
ASHRAE 241non government site opens in new window, 2016 CA Title 24 Standardnon government site opens in new window, Finnish SIAQ “Individual”
~30 CFM/Person
CA Title 24: Greater of 0.15 CFM/SF, 15 CFM/Person
Demand Control Ventilation required
700 ppm
*Note: The relation between ventilation and CO2 is not linear. As CO2 goes down, the same amount of ventilation removes less CO2 each minute. More airflow is needed to remove the 1 ppm of CO2 at 700ppm than at 1000 ppm.
How might more fresh air benefit people?

According to a significant body of research, more fresh air is better for our health. Higher ventilation rates supplying more outdoor air are associated with less absenteeism, fewer symptoms of sick building syndrome, and better performance on standardized cognitive tests. Both ventilation rates and expected CO2 levels have been used as measures for this.

Once you select a minimum rate for the building, is air quality always the same?

Designers calculate a building’s ventilation rate based on the maximum number of people they expect, but the nature of indoor environments is much more dynamic. Several factors like contaminants introduced by people, outdoor pollution levels, leaky structures and facades, renovations after construction, and the approach used to distribute air within a space all affect air quality. Still, the number of people in a space can be the most dynamic factor day to day. The more people, the less effective a given ventilation rate will be at maintaining air quality and removing the “bioeffluents” and other contaminants those people bring. Carbon dioxide (CO2) can be measured to show this effect. ASHRAE 62 sets a maximum target for CO2 equal to the quantity of CO2 in outdoor air plus 700ppm. Since there is usually about 400-500ppm CO2 in outdoor air conventional ventilation rates should keep indoor CO2 below ~1,200ppm. However the dynamic factors present in the building mean that the designer’s initial calculation alone is not enough. To optimize a building’s indoor environment so that it enhances health, comfort and performance requires continuous, distributed measurement and adaptive management.

What should we consider when designing fresh air rates for new or retrofit space?

GSA’s Total Workplace Scorecard (to be deployed summer 2020; requests can be sent to AskFMI@gsa.gov) lists a number of factors believed to contribute to improving indoor air quality and increasing the effectiveness of ventilation systems. Here are a few things to consider when designing new systems or renovating existing systems:


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Lever 2 - Remove Outdoor Pollutants

decorative imageSource: USGSopens in new window, photographed by EPA

Indoor air quality is influenced by outdoor air pollutants. Of these, fine particulate matter (PM) and ozone (O3) account for much of the adverse health effects associated with air pollution. Importantly, most of our exposure to these pollutants actually occurs where they are brought indoors.17 Most commercial office buildings use filters to remove PM from outdoor air and some, though many fewer, use filters with activated carbon to remove O3.

Wide ranges of outdoor air pollution can be found across the U.S. Generally, higher PM and O3 levels are found in urban areas. PM forms directly as a by-product of combustion in cars, buildings and industrial processes while O3 forms after volatile organic compounds released from these same sources go through chemical changes in the air. Periodic or seasonal events like wildfires can cause dramatic, if temporary increases across a whole region as seen in the wildfires in California in 2017 and 2018. Significant local variations can also be found due to placement of industrial facilities or major traffic arteries within a given region.

The table below provides a summary of approaches to building air filtration that help protect the indoor air we breathe from outdoor pollutants. The higher the MERV rating of a building’s filters, the more outdoor air pollution you can have and still provide good air quality indoors. Filters must be properly maintained, however, to get this benefit as dirty higher-MERV filters can actually be worse for people than clean lower-MERV filters. Outdoor air infiltration can also be reduced by using building systems to maintain positive pressure conditions. This can reduce PM infiltration through the building envelope.

How much filtration do existing approaches suggest?
Outdoor Pollutant Levels Conventional "Good" Indoor Levels Enhanced "Better"
Indoor Levels
Stringent "Best"
Indoor Levels
If outdoor 8-Hour average levels are:
Prescriptive: MERV 8
Removes ~30% of PM
ASHRAE 62non government site opens in new window
Prescriptive: MERV 13
Removes ~60% of PM
LEED v4non government site opens in new window / Well v2non government site opens in new window
Performance: Stay below 12-15 μg/m3
RESET Highnon government site opens in new window / Well v2non government site opens in new window
0 - 20 μg/m3 *
Most U.S. urban areas in typical pollution conditions
0 - 14 μg/m3 0 - 8 μg/m3 <12-15 μg/m3
or 75% less than outdoors
20 - 50 μg/m3 *
U.S. urban areas in peak pollution conditions
14 - 35 μg/m3 6 - 20 μg/m3 <12-15 μg/m3
or 75% less than outdoors
50 - 100+ μg/m3 *
Some overseas urban, extreme events
35 - 90+ μg/m3 20 - 40+ μg/m3 <12-15 μg/m3
or 75% less than outdoors
Expansion space Install sufficient rack space to respond to extreme events
Well v2non government site opens in new window
Ozone & VOCs No benefit Activated Carbonnon government site opens in new window
Removal of ozone / VOCs
Well v2non government site opens in new window
Activated Carbonnon government site opens in new window
Removal of ozone / VOCs
Well v2non government site opens in new window
Airborne Pathogens No benefit Ultraviolet
Germicidal irradiation
Sanitizes air of pathogens
Well v2non government site opens in new window
Germicidal irradiation
Sanitizes air of pathogens
Well v2non government site opens in new window
*Note: This table considers the indoor environment that different approaches to filtration provide. RED text means NAAQS 8 hour average standards of 35 μg/m3 are not met indoors. Yellow means NAAQS 8 hour average is met but RESET High Performance 8 hour average is not. Black means both are met.
How might more filtration and less indoor pollution benefit our health?

Enhanced and stringent approaches to filtration will result in better indoor air quality. Approaches that provide some flexibility to prescriptive requirements or that are performance-based may also save energy while providing those health benefits.


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Lever 3 -  Manage Thermal Conditions

The Six Factors Affecting Individual Thermal Comfort: Air Temperature, Air Speed, Relative Humidity, Radiant Temperature, Metabolic Activity, and Personal Clothing

Thermal conditions in office buildings are generally viewed from the perspective of comfort rather than health. Priority is placed on maintaining uniform conditions that can't meet the wide range of personal factors and preferences people have. While there are six factors that affect thermal comfort most buildings use only air temperature to manage indoor conditions. Perhaps we create suboptimal indoor environments by avoiding variation and ignoring the influence of other factors like humidity on health. The limitations to our conventional approach are evident in the fact that ASHRAE 55 standard for thermal comfort accepts as success receiving complaints from 1 in 5 occupants that conditions are too hot or too cold.

Temperature studies have found that performance of office work tasks is maximized when air temperature is approximately between 70 °F to 73 °F, with a peak at 71°F. As indoor air temperatures fluctuate from this range, estimates put performance decreases at 0.37% and 0.43% per each degree decrease or increase, respectfully.20

After temperature, humidity has the most significant impact on health and performance. However, it has little direct impact on results in comfort surveys. Human beings have no direct ability to sense RH and perceive it instead as discomfort with temperature or as “stuffy” air. While high-humidity leads to significant, often visible, mold and other microbial growth, dry air’s issues are generally unfelt and unseen. For this reason, lower bounds for RH have been gradually removed from ASHRAE standards for comfort and ventilation. Poor experience with humidification in older building system designs has made many designers wary of actively addressing dry air. However, improved design and equipment and an emerging body of research supports testing methods to tighten control of RH around an optimal range.

Approach RH Range
(at ~72°F)
Environmental / Health Outcome
Conventional (Good):
Maintain <60% RH Mold and microbial growth are prevented avoiding serious acute and long-term health impacts

Dry air driven by weather and indoor heating:
  • PM counts, infectious droplet size, and the time both remain in air increase as RH drops below 40%
  • Inflammation of eyes, skin and airways, greater sensitivity to PM and VOCs, and greater susceptibility to infection occur in minutes of RH below 40%
  • Dehydration, fatigue and loss of focus begin to affect people over a few hours of RH below 40%
Enhanced (Better):
Illinois IDPH
Maintain 20%-60% RH
Dry air varies with weather but avoids extremes:
  • PM counts are reduced, smaller infectious droplets, and the time both remain in air is less
  • Inflammation, dehydration and related effects still occur but the impacts are less severe and frequent
  • Care must be taken to avoid condensation within the building envelope in cold climates or during colder conditions
Stringent (Best):
ASHRAE Japan (Healthcare)
Maintain 40%-60% RH
RH maintained within a tight range:
  • Less PM and potentially less filtration needed to maintain air quality
  • RH does not drive inflammation or dehydration
  • Reduced risk of infection from pathogens
  • Care must be taken to avoid condensation within the building envelope in cold climates or during very cold conditions
If there is an optimal range for temperature, is there also an optimal range for RH?

A growing body of research has found evidence of an optimal range for RH between 40-60%. Researchers with GSA, the University of Arizona and Baylor College of Medicinenon government site opens in new window found higher stress and poorer sleep qualitynon government site opens in new window outside this range.21 While the impacts of high indoor RH are accepted and often visible, low RH or dry air is increasingly seen as important as well.

Typical impacts of dry air include:

How can we manage thermal conditions to improve occupant health?

decorative image We can improve the building envelope to reduce uncomfortable conditions shown to affect performance. Eliminate hot or cold walls and windows by improving insulation, reduce direct solar gain through windows with appropriate shading and Solar Heat Gain Coefficient (SHGC), and eliminating drafts around windows and doors.

We can actively manage RH, provide greater individual control and choice in temperature, and monitor room-level conditions to prompt behavioral interventions.


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Lever 4 - Eliminate Indoor Contaminants

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While outdoor air pollutants can contribute a lot to poor indoor air quality, contaminants are introduced by the things people bring into the building as well. So-called “source control” is critical to maintaining healthy indoor air and should be addressed through building design, purchasing policy and educating building occupants on the impacts of their behavior. Source control is especially important in avoiding concentrations of Volatile Organic Compounds (VOCs) which are often introduced by new furnishings, construction and renovation activities, administrative processes including cleaning and print/copy activities, personal items like food, disinfectant and other aerosols, poor hygiene, and personal care products. Particulate matter (PM) contaminants are also introduced through ventilation, infiltration, and occupant movement and activity.

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GSA wishes to thank the following contributors for their input to the Wellbuilt for Wellbeingopens in new window project:

  • Seema Bhangar, Ph.D., WeWork, Inc.
  • Alyse Falconer, PE, Point Energy Innovations
  • Traci Hanegan, PE, ASHRAE Fellow, Coffman Engineers, Inc.
  • Kevin Keene, LEED-AP, Pacific Northwest National Laboratory
  • Luke Leung, PE, LEED Fellow, Skidmore, Owings and Merrill, LLP
  • Casey Lindberg, Ph.D., HKS Inc.
  • Vivian Loftness, FAIA, Carnegie Mellon University
  • Forrest Meggers, Ph.D., Princeton University
  • Shona O’Dea, WELL-AP, RESET AP, DLR Group, Inc.
  • Jovan Pantelic, Ph.D., University of California at Berkeley
  • Chris Pyke, Ph.D., LEED Fellow, ArcSkoru
  • Z Smith, FAIA, Eskew+Dumez+Ripple, APC
  • Stephanie Taylor, M.D., Taylor Healthcare Consulting
  • Nora Wang, Ph.D.. Pacific Northwest National Laboratory


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Page last updated 08/31/2020
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Related Topics

Adaptive Thermal Comfort

Adaptive Thermal Comfort is the theory that occupants can adapt to be comfortable at a variety of temperatures. Since comfort is based on many factors, including air speed, humidity, and temperature, adaptive thermal comfort strives to connect occupants to the outdoor world, and empower them to feel comfortable in their environments.

BuildingGreen.com | Thermal Comfortnon government site opens in new window

Adequate Ventilation and Exhaust

Adequate ventilation and exhaust is important to prevent build-up of odors, carbon dioxide, allergens and toxins in indoor air. Provide separate exhaust for copy, printing, break rooms, and food preparation areas. Flush out occupied spaces prior to occupancy. Use energy efficient or variable drive fans for enhanced air movement. Consider bringing in more fresh air into the building. Ensure the building management staff is conducting preventive maintenance on all building exhaust systems (restrooms, garage exhaust fans, etc). Seal ventilation duct opening during construction or renovations to reduce dust and particle build-up.

Air Contaminants

Air contaminants are any substances in the air, particulate or gaseous, which pollute the air and make it hazardous to human health. Good indoor air quality management techniques seek to reduce the amount of contaminants in the air and protect the health of vulnerable building occupants.

Entryway Systems/Walk-off Mats

Toxins are tracked into a building on occupants’ shoes. Entryway systems, like grates, grills, and walk-off mats can greatly reduce the amount of outside dirt, dust, and particulates brought into the building. This makes for a cleaner environment, and cuts down on the amount of cleaning necessary to maintain a high level of cleanliness in the facility.

Healthy Buildings

Health, as defined by World Health Organization in its 1948 constitution, is “a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity”. This definition of health has been expanded in recent years to include (1) resilience and the ability to cope with health problems and (2) the capacity to return to an equilibrium state after health challenges.

These three health domains - physical, psychological, and social - are not mutually exclusive but rather interact to create a sense of health that changes over time and place. The challenge for building design and operations is to identify cost-effective ways to eliminate health risks while also providing positive physical, psychological, and social supports as well as coping resources.

Learn more about Buildings and Health.

Heating, Ventilating and Air Conditioning (HVAC)

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Whole Building Design Guide | High-Performance HVACnon government site opens in new window

Outside Air

Outside air is fresh air that comes into the facility as supply air. It is mixed with air already conditioned in the space.

Replacement air

Outdoor air that is used to replace air removed from a building through an exhaust system. Replacement air may be derived from one or more of the following: makeup air, supply air, transfer air, and infiltration. However, the ultimate source of all replacement air is outdoor air. When replacement air exceeds exhaust, the result is exfiltration.

Sick Building Syndrome (SBS)

When occupants feel sick at work, but not elsewhere, they likely have SBS. SBS often manifests as cold or flu-like symptoms after breathing stale or contaminated air. It harms worker productivity and morale. It may also increase absenteeism and worker turnover. See EPA's Sick Building Syndrome Factsheetopens in new window for more information.

Supply Air

Supply air is air delivered to a space by mechanical ventilation.  It can be 100% outside air, or it can be a combination of outdoor air, recirculated air and / or transfer air.  Although it may seem like a good idea to use 100% outside air, the air needs to be conditioned (heated or cooled) before it can be circulated, so it makes sense to use only as much as is necessary to keep the circulating air fresh and the energy use down.

Thermal Comfort

Workspaces should be designed to provide the optimum level of thermal comfort for the occupants. Occupant comfort should be based on ASHRAE Standard 55.

ASHRAE.org | Standards 62.1 and 62.2non government site opens in new window


Ventilating is the process of "changing" or replacing air in any space to replenish oxygen, control temperature, and remove moisture, odors, smoke, heat, dust, airborne bacteria, and carbon dioxide. Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in a building.


Ventilation is the process of "changing" or replacing air in any space to control temperature; remove moisture, odors, smoke, heat, dust, airborne bacteria, and carbon dioxide; and to replenish oxygen. Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings.

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