Indoor Air Quality 

Resource Description

IAQ & Human Comfort

Indoor air quality (IAQ) depends on the building usage, applied ventilation solutions, building location, construction methods and materials, and outdoor conditions. Adequate ventilation and healthy structures are prerequisites for good indoor air quality. Poor air quality may cause tiredness, inability to concentrate, and even illness (i.e., Sick Building Syndrome).

Human comfort, productivity, and a sense of health and well-being are the positive outcome of a healthy indoor environment. Human comfort depends on the interaction of multiple variables. Optimizing both temperature and relative humidity satisfies the comfort requirements for a wider variety of occupants than optimizing only temperature. Carbon dioxide (CO2) level is a surrogate measurement for indoor air quality and human presence. Air quality meters/monitors - are the instruments that are ideal for monitoring indoor air quality in crowded public spaces with potentially high levels of CO2 (carbon dioxide) such as offices, factories, classrooms, hospitals, and hotels.

Sick Building Syndrome
Indoor Air Quality (IAQ)


Why Measure CO2

An increasingly dangerous trend in home and building Energy Audits focus solely on the “Energy Efficiency” of the building while ignoring the potential risks of sealing “IN” CO2 emissions and moisture in the home causing serious health and comfort concerns. By sealing your home to be “Air Tight” for the purpose of decreasing gas and electric bills, you could also be making our buildings TOO TIGHT. In many cases, the benefits associated with a drop of energy usage carry a heavy price in the form of moisture damage and health risks produced by higher levels of CO2.

Until very recently, houses were designed and built with the concept of “A house should be allowed to breathe”. This self-ventilation strategy would provide for constant replenishment of the air supply to the occupants by balancing the quality of indoor “used” air (higher levels of CO2 and moisture), with “fresh” outside air (higher levels of oxygen).

Starting around the early 2000s, there has been a strong emphasis toward energy savings and the importance of reducing the individual’s carbon footprint. In addition, newer technologies including strong foam insulation, high-efficiency windows, and airtight doors, among many others, have brought a push for TIGHT BUILDINGS by sealing homes and buildings from outside air. While these initiatives may be monetarily efficient, there is now a growing concern about the actual indoor air quality of the buildings and their effects on the health of their occupants, especially the young and elderly.

By making buildings too tight, we are locking in all of the pollutants generated inside the house (CO2, CO, smoke, odors, germs, VOCs, etc.). Those chemicals, if not dealt with carefully with an intelligent ventilation system, could make the premises very uncomfortable for the residents. Furthermore, people and pets could become drowsy, get sick more frequently, and have potentially fatal consequences in extreme cases.

The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) created a standard (62.2) whereby they recommend a certain amount of air changes in the home depending on the size of the home and how many people live there.

CO2 Sources and Levels

Measuring CO2 is a simple, fast and effective way of determining the Indoor Air Quality and the effectiveness of the building’s ventilation system. A well-designed ventilation system is extremely important for diluting high CO2 levels and circulate clean fresh air back into the home or building. High CO2 readings are a MAJOR indication of poor ventilation, which could also signal a build-up of other air contaminants.

Indoor CO2 levels are directly affected and elevated by a number of sources including but not limited to the following:

  • Number of people and animals in a building
  • Gas & fuel burning appliances (Heating system, water heaters, dryers, etc.)
  • Wood fireplaces and stoves
  • Cigarettes
  • Outside sources (Nearby highways, parking garages, industrial sources, etc.)

Levels of CO2 in the Air and Associated Health Effects



350 - 450 ppm

Typical atmospheric concentration / Background (normal) outdoor air level.

450 - 1,000 ppm

Acceptable IAQ. Typical level found in occupied spaces with optimal air exchange.

about 1,000 ppm

Tolerable indoor air quality.

1,000 - 2,000 ppm

Level associated with complaints of drowsiness and poor air.

2,000 - 5,000 ppm

Level associated with headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate, and slight nausea may be present.

>5,000 ppm

This indicates unusual air conditions where high levels of other gases could also be present. Toxicity or oxygen deprivation could occur. This is the permissible exposure limit for daily workplace exposures.

3 - 8%

Increased respiration rate, headache.

> 10%

Nausea, vomiting, unconsciousness.

> 20%

Rapid unconsciousness, death.


Optimal Locations for CO2 Transmitters (Air quality monitors)

  • Avoid locations where people may breathe directly onto the sensor. Also avoid placing sensors close to intake or exhaust ducts, or near windows and doorways.
  • In demand controlled ventilation, wall-mounted sensors provide more accurate data on ventilation effectiveness than duct-mounted sensors. Duct-mounted sensors are best suited to single-zone systems and should be installed as close to the occupied space as possible to allow for easy maintenance access.
  • When measuring CO2 for the purposes of personnel safety, transmitters should be installed close to potential leakage points to enable early detection. The geometry, ventilation, and airflow of the monitored area need to be taken into account. The number and location of the CO2 transmitters should be based on a risk assessment.
clean air - healthy home


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