The short answer
| Task | Typical frequency in a commercial building |
|---|---|
| Filter change | 2–4 times a year, depending on filter class, dust levels and pressure drop |
| Ventilation unit servicing | 1–2 times a year; quarterly for large systems |
| Duct condition check | visual inspection once a year; cleaning as required |
| Restaurant extract hoods and grease filters | considerably more often — depending on load |
The exact frequency is set by the unit's manufacturer, the use of the premises and the load on the system. The table reflects typical practice, not a regulatory requirement.
Filter changes
The filter is the first place where ventilation starts to underperform. A clogged filter reduces airflow, increases the fans' energy consumption and can let dust into the ductwork.
Modern ventilation units have pressure-drop monitoring or controls that warn when a filter needs changing. Where there are none, filters are changed to a schedule — typically 2 to 4 times a year. In spring (pollen) and next to a busy street, filters clog faster.
What servicing a ventilation unit involves
- filter replacement and cleaning of the filter sections;
- checking fans, belts and bearings;
- cleaning the heat exchanger (heat recovery unit) and checking it is working;
- checking the heater and cooler, cleaning the condensate drain;
- checking that dampers and actuators operate;
- checking the control settings, temperatures and airflow;
- a maintenance report listing any defects found.
What the regulations require
Latvia's Fire Safety Regulations (Cabinet Regulation No. 238) require the natural ventilation ducts in commercial premises to be cleaned and their technical condition checked at least once every five years (para. 80). A record is drawn up for the cleaning.
The maintenance frequency for mechanical ventilation units is set by the manufacturer and the building's operating requirements. Where ventilation forms part of the fire safety solution (smoke extraction or fire dampers, for example), the maintenance requirements for fire protection systems also apply.
Signs that ventilation is underperforming
- stuffy or humid air in the rooms, tiredness and headaches in the afternoon;
- condensation on windows, mould in corners;
- increased noise or vibration from the unit;
- rooms too hot or too cold even though the settings have not changed;
- higher electricity consumption;
- dirty grilles and diffusers, or dust around them.
Updated 03.10.2026 · ITTU