Ventilation controls indoor air quality by bringing in outdoor air to dilute pollutants and exhausting stale air from the building. Most air quality problems come from too little outdoor air reaching the occupied space, a pollution source that is not being controlled, or a humidity problem, and each can be found with a methodical look at the building and its HVAC system.
What makes indoor air poor
Indoor air carries a mix of contaminants from people, materials and activities:
- Carbon dioxide and body odours from occupants, which rise when ventilation is not keeping up with the number of people.
- Volatile organic compounds from paints, adhesives, furniture, cleaning products and printers.
- Fine particles from outdoor air, wildfire smoke, combustion and indoor activities.
- Combustion gases, including carbon monoxide, from faulty fuel-burning equipment or vehicle exhaust drawn in from parking areas or loading docks.
- Moisture and biological growth from leaks, condensation and wet materials. Our guide on moisture, mould and indoor air covers this in detail.
- Radon, a radioactive soil gas that can enter through foundations.
Three ways to control indoor air quality
- Control the source. Removing or isolating a pollutant is the most effective step. Examples include choosing low-emitting materials, exhausting printer and copy rooms, and fixing leaks quickly.
- Ventilate. Outdoor air dilutes what cannot be removed at the source. Local exhaust in washrooms, kitchens and labs removes pollutants before they spread.
- Filter and clean the air. Filters remove particles from recirculated and outdoor air. See HVAC filters and MERV ratings.
How much ventilation is enough
Building codes across Canada set minimum ventilation requirements, and for most commercial buildings they reference ASHRAE 62.1, which calculates outdoor air based on both the number of people and the floor area of each space. Residential buildings follow separate requirements. The design rate is only a starting point: what matters is how much outdoor air the system actually delivers to occupied spaces, which can drift well away from the design over time.
Common ventilation failures
- Outdoor air dampers stuck closed, or set to a minimum position that was never verified.
- Economizer controls disabled or broken.
- Fans scheduled off during occupied hours, or ventilation reduced to save energy without checking the effect.
- Rooms subdivided or used by more people than the design assumed.
- Supply air short-circuiting from diffuser to return without mixing into the occupied zone.
- Outdoor air intakes placed near exhaust outlets, loading docks or garbage areas.
- Exhaust fans that have failed or have blocked grilles.
What to measure
A focused set of measurements tells you a lot:
| Measurement | What it can tell you |
|---|---|
| Carbon dioxide | Whether ventilation is keeping up with occupancy. It is an indicator of ventilation, not a measure of all pollutants. |
| Temperature and relative humidity | Comfort, and conditions that may favour condensation or mould |
| Outdoor airflow at air handlers | Whether design ventilation is actually being delivered |
| Particles | Effect of filtration and outdoor sources such as wildfire smoke |
| Carbon monoxide | Combustion problems or vehicle exhaust entering the building |
Measure during normal occupancy, and over time rather than in a single spot reading. Trends across a working day reveal much more than one number.
Suspected carbon monoxide or gas. If people report headaches, dizziness or nausea that ease when they leave, or a CO alarm sounds, evacuate and call emergency services. Do not wait for an air quality study.
A practical approach to complaints
- Record complaints: who, where, when and what symptoms or odours.
- Walk the affected area and look for obvious sources, water damage, blocked vents and changes in use.
- Check the HVAC equipment serving that area: outdoor air dampers, filters, schedules, drain pans and exhaust.
- Take measurements over time during occupied hours.
- Fix what you find, then follow up with the occupants to confirm the problem is solved.
Many complaints are solved at steps 2 and 3. If they are not, specialist sampling may be needed.
Balancing air quality and energy
Outdoor air has to be heated in winter and cooled in summer, so there is a real energy cost to ventilation. Heat and energy recovery ventilators recover much of it, and demand-controlled ventilation adjusts outdoor air to actual occupancy. Our guide on HRV vs ERV explains the options.
How ehZee can help
Our mechanical system inspections check whether your ventilation equipment is delivering outdoor air as intended, and trace air quality complaints back to the equipment and conditions behind them. You get a written report with findings ranked by priority.
Common questions
Is a high carbon dioxide reading dangerous?
At levels typical in buildings, carbon dioxide is mainly an indicator that ventilation is low compared with occupancy. That often means other pollutants are building up too, which is the bigger concern.
Should we open windows to improve air quality?
Operable windows can help, but they can also upset the HVAC system's pressure balance and let in outdoor pollution or smoke. It is better to fix mechanical ventilation and use windows as a supplement where the building is designed for it.