Ventilation or air conditioning: what is the difference and do you need both?
Why air conditioning does not provide fresh air, how ventilation and heat recovery work alongside it, and what offices, gyms and classrooms need.
Short answer
Air conditioning heats and cools the air already in a room; ventilation replaces it with fresh outdoor air. Most occupied commercial spaces need ventilation to control CO2 and odours, and air conditioning where they overheat — ideally designed together, often with heat recovery.
What each system does
- Air conditioning: controls temperature (and some humidity) by recirculating room air
- Ventilation: supplies fresh air and removes stale air, controlling CO2, odours and moisture
- Heat recovery ventilation: ventilates while recovering much of the heat from extracted air
How much fresh air
Guidance for offices is typically around 10 litres per second per person. Gyms, classrooms and meeting rooms need careful design because occupancy can be high.
Designing them together
Grilles, controls and set points should be coordinated so ventilation air does not fight the air conditioning. CO2 sensors can vary ventilation with occupancy to save energy.
Questions
Do portable air conditioners provide fresh air?
No. They also only treat room air and exhaust heat through a hose.
Will opening windows do?
Sometimes, in small spaces — but not in noisy or polluted locations, and it wastes heat in winter.
Related services
This guide is general information, not legal advice. Rules can change; check the current position with the relevant authority for your building.