Indoor air quality testing and what to measure

Indoor air quality (IAQ) complaints are among the most common calls a facility manager receives: stuffiness, headaches, odours, dry eyes, dust. Some complaints trace back to a single obvious cause, while others involve ventilation, temperature, humidity and pollutant sources interacting. Good IAQ testing is not about buying the most sensitive instrument. It is about measuring the right things, in the right places, at the right time, and comparing them with sensible reference values.

This guide sets out what to measure, what the main Canadian guidelines say, and how to structure an investigation.

Start with the building, not the instruments

Before taking a single reading, gather information:

1. Document the complaints. Where, when, who and what symptoms. Complaints that vary with time of day or occupancy point to ventilation; complaints tied to a location point to local sources.
2. Review the HVAC system. Design outdoor airflow, schedules, economizer controls, filter types and maintenance records.
3. Walk the building. Look for water damage, blocked diffusers, new furnishings or renovations, chemical storage, printers, loading docks near intakes and similar sources.
4. Check the BAS. Trends of outdoor air damper position, supply air temperature, space temperature and CO2 often reveal problems faster than spot measurements. See trend logging and using BAS data.

Only then plan measurements to confirm or rule out likely causes.

Core parameters

Temperature and relative humidity

Thermal discomfort is often reported as poor air quality. Measure dry bulb temperature and relative humidity (RH) at occupied height and compare with ASHRAE Standard 55. RH below about 20 to 30 percent, common in Canadian winters, contributes to dry eye and static complaints; sustained RH above about 60 percent increases the risk of mould and dust mites.

Carbon dioxide

CO2 is primarily an indicator of ventilation per person, not a pollutant at typical indoor levels. Outdoor CO2 is currently a little over 400 ppm. In a densely occupied room, steady-state CO2 rises as ventilation per person falls. ASHRAE 62.1 does not set an indoor CO2 limit, but a rise of roughly 700 ppm above outdoor levels has long been used as a rough indicator that ventilation is in line with typical office rates. Health Canada's residential indoor air quality guideline sets a long-term exposure limit of 1,000 ppm (24-hour average) for homes, which is often used as a reference point elsewhere. Readings well above 1,000 ppm in occupied commercial spaces warrant a closer look at outdoor airflow.

Particulate matter

Fine particulate (PM2.5) affects respiratory and cardiovascular health. Indoor PM2.5 comes from outdoor air, especially during wildfire smoke events and near traffic, and from indoor sources such as cooking, printers and construction. Optical particle counters and low-cost sensors are useful for trends and comparisons, though their absolute accuracy varies. Health Canada recommends keeping indoor fine particulate as low as reasonably achievable.

Carbon monoxide

CO comes from combustion: vehicle exhaust from garages and loading docks, and malfunctioning gas appliances. Any persistent indoor CO above outdoor background deserves investigation. Health Canada publishes residential exposure limits for CO, and provincial occupational health and safety regulations set workplace limits.

Volatile organic compounds and formaldehyde

VOCs come from paints, adhesives, furniture, cleaning products and personal care products. Handheld photoionization detectors give a total VOC (TVOC) reading useful for finding sources but not for health comparisons, because TVOC is a mixture with no single guideline. For specific compounds, sorbent tube or canister sampling with laboratory analysis is required. Formaldehyde has its own Health Canada residential guideline: 50 µg/m3 for long-term (8-hour) exposure and 123 µg/m3 for short-term (1-hour) exposure.

Radon

Radon is a naturally occurring radioactive gas that enters through foundations. Health Canada's guideline is 200 Bq/m3, and testing is done with long-term detectors over at least three months, ideally during the heating season. Radon is mostly a concern in basements and ground-floor spaces of buildings in high-radon areas.

Biological contaminants

Mould is best investigated visually and with moisture measurements first. Air sampling for spores can support an investigation but is difficult to interpret alone. Health Canada's position is that visible mould and dampness should be remediated regardless of airborne counts.

Summary of reference values

Workplace exposure limits are set provincially and differ across Canada, so occupational assessments should reference the applicable provincial regulation.

Instruments and methods

• Direct-reading monitors for temperature, RH, CO2, CO and PM2.5 are suitable for continuous logging over a week or more. Choose CO2 sensors with non-dispersive infrared (NDIR) technology and verify calibration before use.
• Integrated sampling with laboratory analysis is needed for specific VOCs, formaldehyde and other compounds.
• Airflow measurement with capture hoods, pitot traverses and thermal anemometers confirms whether outdoor air and supply airflow match design. Many IAQ problems are ventilation problems that only a balancing measurement will confirm.
• Pressure measurements between spaces confirm that washrooms, kitchens and other sources are negative relative to occupied areas.

Measure during normal occupancy, at breathing height (roughly 1.1 m (3.5 ft) seated), and away from direct supply air, windows and occupants' breath. Always record outdoor conditions at the same time for comparison.

Interpreting results

A single number rarely tells the story. Look for patterns:

• CO2 rising steadily through the day and dropping at lunch points to low ventilation for the occupancy.
• High PM2.5 that tracks outdoor readings points to filtration or intake issues; peaks during working hours suggest indoor sources.
• TVOC spikes after cleaning or near new furniture suggest source control and flush-out rather than more ventilation.
• Odours that appear in specific wind conditions often trace to exhaust re-entrainment.

Report findings with the measurement method, location, duration and reference values used, and recommend corrective action. Corrective work often involves rebalancing outdoor air, fixing economizer controls, upgrading filters or adjusting schedules, which is where retro-commissioning fits naturally.

Key takeaways

• Investigate the building, complaints and HVAC operation before measuring.
• Temperature, RH, CO2, PM2.5, CO and specific VOCs are the core parameters for most commercial investigations.
• CO2 is a ventilation indicator, not a direct health measure at typical indoor levels.
• Health Canada guidelines and provincial OHS regulations are the main Canadian references.
• Airflow and pressure measurements often confirm the root cause better than pollutant readings alone.