Comparison
AHU or mechanical ventilation: what is the difference, and which should you choose?
A mechanical ventilation system renews the air: it extracts stale air and introduces fresh air, without treating it. An air handling unit (AHU) goes further: through its filtration stages, its heat exchanger and its control system, it filters, heats, cools, humidifies or dehumidifies the air before supplying it. The difference shows in the airflows too: an AHU typically covers 1,000 to 50,000 m³/h for commercial and industrial buildings, whereas a 100 m² house needs only 150 to 300 m³/h. In practice: mechanical ventilation for housing and small premises, an AHU as soon as temperature, humidity or air quality have to be controlled.
AHU versus mechanical ventilation
| Criterion | Mechanical ventilation | Air handling unit |
|---|---|---|
| Primary function | Renew the air (extract + fresh air) | Renew and treat the air |
| Air treatment | Basic filtration | Staged filtration, heating, cooling, humidification, dehumidification |
| Typical airflows | 150 – 300 m³/h for a 100 m² dwelling | 1,000 – 50,000 m³/h |
| Control | Simple, often humidity-driven | Full control (temperature, humidity, air quality) |
| Target buildings | Housing, small commercial premises | Offices, public buildings, healthcare, food processing, industry |
| Heat recovery | Supply-and-extract: possible | Exchanger able to recover a large share of the extract air energy |
When an AHU is the right answer
An AHU becomes necessary as soon as the supply air has to meet a specific requirement rather than simply being 'renewed'.
- Densely occupied commercial spaces: open-plan offices, meeting rooms, public-access buildings.
- Sensitive environments: clinics, laboratories, cleanrooms, where the filtration class is mandated.
- Food processing and pharmaceutical industry: humidity control and positive pressure in clean zones.
- Industrial processes that need a stable temperature or humidity all year round.
- Buildings where heat recovery from the extract air has to be exploited.
When mechanical ventilation is enough
Fitting an AHU in a space that does not need one wastes both capital and energy. Conversely, fitting simple mechanical ventilation where an AHU is required creates a health risk and a compliance risk. Mechanical ventilation remains the right choice for housing, small retail units, washrooms and service rooms, where the job is limited to removing moisture and odours.
Extract-only or supply-and-extract?
- Extract-only: mechanical extraction with passive air inlets. Lower capital cost, no heat recovery.
- Supply-and-extract: mechanical extraction and supply through a heat exchanger, recovering a large share of the heat (or the coolth) in the extract air — a clear benefit in Moroccan cities with wide temperature swings such as Fez or Marrakesh.
- Supply-and-extract AHU: the same principle at building scale, with heating and cooling coils, optional humidification and full control.
What to have ready before choosing
- Floor area, volume and ceiling height of the spaces served.
- Occupancy and the hours during which the space is used.
- Temperature and humidity constraints tied to the activity.
- Filtration class required by the sector (healthcare, food processing and so on).
- Space available for the unit and routes for the ductwork.
Frequently asked questions
What is the difference between an AHU and a mechanical ventilation system?
A mechanical ventilation system renews the air by extracting stale air and introducing fresh air, without really treating it. An air handling unit filters, heats, cools, humidifies or dehumidifies the air before supplying it, using its filtration stages, its heat exchanger and its control system. The AHU serves commercial buildings and industry, mechanical ventilation serves housing and small premises.
What airflow does an air handling unit cover?
Air handling units typically cover airflows of 1,000 to 50,000 m³/h, the scale of a commercial or industrial building. By comparison, a 100 m² house needs only 150 to 300 m³/h, which is mechanical ventilation territory.
Can an AHU be installed in a house?
Technically yes, but it is out of proportion: the minimum airflow of an AHU is several times a dwelling's requirement, and neither the footprint nor the running cost is justified. A supply-and-extract mechanical ventilation system already delivers the heat recovery being sought at domestic scale.
Can an AHU replace air conditioning?
An AHU fitted with heating and cooling coils does provide thermal treatment of the fresh air and can cover all or part of a commercial building's requirement. In many projects it is nonetheless paired with terminal units (cassettes, ducted units, fan coils) that deal with internal gains room by room.
Further reading
Our AHU range for commercial buildings and industry.
Read more Air treatment serviceFiltration, humidity control and indoor air quality.
Read more Air filter classes G4, F7, HEPAChoosing the filtration stages for your unit.
Read more Food processing ventilationPositive pressure, humidity and microbiological control.
Read more